TWI782985B - Positive electrode active material, method for manufacturing positive electrode active material, and secondary battery - Google Patents

Abstract

A positive electrode active material having high capacity and excellent cycle performance is provided. The positive electrode active material has a small difference in a 5 crystal structure between the charged state and the discharged state. For example, the crystal structure and volume of the positive electrode active material, which has a layered rock-salt crystal structure in the discharged state and a pseudo-spinel crystal structure in the charged state at a high voltage of approximately 4.6 V, are less likely to be changed by charge and discharge as compared with those of a known positive electrode active material.

Description

Positive electrode active material, method for producing positive electrode active material, and secondary battery

One embodiment of the invention relates to an article, method or method of manufacture. In addition, the present invention relates to a process (process), machine (machine), product (manufacture) or composition (composition of matter). One embodiment of the present invention relates to a semiconductor device, a display device, a light emitting device, an electrical storage device, a lighting device, an electronic device, or a method for manufacturing them. In particular, one embodiment of the present invention relates to a positive electrode active material usable for a secondary battery, a secondary battery, and an electronic device including the secondary battery.

Note that in this specification, the power storage device refers to all elements and devices that have a power storage function. For example, storage batteries such as lithium-ion secondary batteries (also referred to as secondary batteries), lithium-ion capacitors, electric double-layer capacitors, and the like are included in the category of power storage devices.

Note that in this specification, an electronic device refers to all devices having a power storage device, and electro-optic devices having a power storage device, information terminal devices having a power storage device, and the like are all electronic devices.

In recent years, development of various power storage devices such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries has been active. In particular, with portable information terminals such as mobile phones, smart phones, and laptop personal computers, portable music players, digital cameras, medical equipment, new-generation clean energy vehicles (hybrid electric vehicles (HEV), electric With the development of the semiconductor industry such as automobiles (EV) and plug-in hybrid electric vehicles (PHEV), etc., the demand for lithium-ion secondary batteries with high output and high energy density has increased sharply, and as a rechargeable energy supply source, it has become Necessities of modern information society.

As characteristics currently required of lithium-ion secondary batteries, higher energy density, improvement in cycle characteristics, improvement in safety and long-term reliability in various operating environments, and the like can be cited.

Therefore, positive electrode active materials for improving the cycle characteristics and increasing the capacity of lithium-ion secondary batteries are being studied (Patent Document 1, Patent Document 2, and Non-Patent Document 1). In addition, studies on the crystal structure of positive electrode active materials have also been conducted (Non-Patent Document 2 to Non-Patent Document 4).

[Patent Document 1] Japanese Patent Application Publication No. 2006-164758 [Patent Document 2] Japanese Patent Application Publication No. 2014-523840

[Non-Patent Document 1] Jae-Hyun Shim et al, "Characterization of Spinel Li _x Co ₂ O ₄ -Coated LiCoO ₂ Prepared with Post-Thermal Treatment as a Cathode Material for Lithium Ion Batteries", CHEMISTRY OF MATERIALS, 2015, 27 , pp.3273-3279 [Non-Patent Document 2] Toyoki Okumura et al, "Correlation of lithium ion distribution and X-ray absorption near-edge structure in O3-and O2-lithium cobalt oxides from first-principle calculation", Journal of Materials Chemistry, 2012, 22, pp.17340-17348 [Non-Patent Document 3] T. Motohashi et al, “Electronic phase diagram of the layered cobalt oxide system Li x CoO ₂ (0.0≤ x ≤1.0)”, Physical Review B , 80(16); 165114 [Non-Patent Document 4] Zhaohui Chen et al, “Staging Phase Transitions in Li x CoO ₂ , Journal of The Electrochemical Society, 2002, 149(12)A1604-A1609

One of the objects of one embodiment of the present invention is to provide a positive electrode active material for a lithium ion secondary battery with a large capacity and excellent charge-discharge cycle characteristics. Another object of one embodiment of the present invention is to provide a positive electrode active material that suppresses capacity reduction in charge and discharge cycles by being used in a lithium ion secondary battery. In addition, one of the objects of one embodiment of the present invention is to provide a high-capacity secondary battery. Another object of one embodiment of the present invention is to provide a secondary battery having excellent charge and discharge characteristics. Another object of one embodiment of the present invention is to provide a secondary battery with high safety and reliability.

Another object of one embodiment of the present invention is to provide a novel material, active material particles, electrical storage device, or a method for producing them.

Note that the description of these purposes does not prevent the existence of other purposes. An embodiment of the present invention does not need to achieve all of the above objects. In addition, objects other than the above-mentioned objects may be extracted from the specification, drawings, and descriptions of claims.

In order to achieve the above objects, the positive electrode active material according to one embodiment of the present invention has little change in crystal structure between a charged state and a discharged state.

One embodiment of the present invention is a secondary battery including a positive electrode and a negative electrode, wherein when the XRD pattern of the positive electrode is analyzed by Rietveld analysis (Rietveld analysis), the positive electrode has a pseudo-spinel crystal structure and the pseudo-spinel The ratio of the spar type crystal structure is 60 wt% or more.

Another embodiment of the present invention is a positive electrode active material containing lithium, cobalt, magnesium, oxygen, and fluorine. After charging a lithium ion secondary battery using a positive electrode active material for the positive electrode and a lithium metal for the negative electrode in an environment of 25°C until the battery voltage becomes 4.6V and the current value is sufficiently low, by using CuKa1 wire powder When analyzed by X-ray diffraction analysis (powder X-ray diffraction), there are diffraction peaks at 2q of 19.30±0.20° and 2q of 45.55±0.10°.

Another embodiment of the present invention is a positive electrode active material, including lithium, cobalt, magnesium, oxygen, and fluorine, wherein the proportion of the positive electrode active material with a charge depth of 0.8 or more is 60 wt% or more per unit cell of the crystalline structure The difference between the volume and the volume per unit cell of the crystal structure having a proportion of 60 wt % or more in the positive electrode active material having a depth of charge of 0.06 or less is within 2.5%.

The aforementioned positive electrode active material preferably contains at least one of Ti and Al.

According to one embodiment of the present invention, a positive electrode active material for a lithium ion secondary battery having a large capacity and excellent charge-discharge cycle characteristics can be provided. In addition, according to one embodiment of the present invention, it is possible to provide a positive electrode active material that suppresses capacity reduction in charge and discharge cycles by being used in a lithium ion secondary battery. In addition, according to one embodiment of the present invention, a high-capacity secondary battery can be provided. In addition, according to one embodiment of the present invention, a secondary battery having excellent charge and discharge characteristics can be provided. In addition, according to one embodiment of the present invention, a secondary battery with high safety and reliability can be provided. According to one embodiment of the present invention, a novel material, active material particles, an electrical storage device, or a method for producing them can be provided.

Note that the description of the above effects does not prevent the existence of other effects. Furthermore, one embodiment of the present invention does not necessarily have all the above-mentioned effects. In addition, there are obviously effects other than the above-mentioned effects in the descriptions of the specification, drawings, and patent claims, and effects other than the above-mentioned effects can be derived from the descriptions of the specification, drawings, and patent claims.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the following description, and a person skilled in the art can easily understand the fact that its modes and details can be changed into various forms. In addition, the present invention should not be construed as being limited only to the contents described in the following embodiments.

In this specification and the like, crystal planes and orientations are represented by Miller indices. In crystallography, numbers are marked with superscripts to indicate crystal planes and orientations. However, in this specification and the like, due to the limitation of symbols in the patent application, - (minus sign) may be added before the digits to indicate crystal planes and orientations, instead of adding a superscript to the numbers. In addition, "[ ]" indicates individual orientations showing the orientation in the crystal, "á ñ" indicates the aggregate orientations of all equivalent crystal orientations, "()" indicates individual planes showing crystal planes, and "{ }" means a collection surface with equivalent symmetry.

In this specification and the like, segregation refers to a phenomenon in which a certain element (for example, B) is spatially unevenly distributed in a solid containing a plurality of elements (for example, A, B, C).

In this specification and the like, the surface portion of particles of an active material or the like refers to a region within a range from the surface to about 10 nm. A face where a split or crack occurs may also be referred to as a surface. In addition, the region deeper than the surface part is called the inside.

In this specification etc., the layered rock-salt type crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure having a rock-salt type ion arrangement in which cations and anions are alternately arranged, and transition metals and lithium are regularly arranged Instead, a two-dimensional plane is formed, so that lithium can be diffused two-dimensionally therein. In addition, defects such as cation or anion vacancies may be included. Strictly speaking, the layered rock-salt crystal structure may be a lattice-distorted structure of the rock-salt crystal.

In addition, in this specification and the like, the rock salt type crystal structure refers to a structure in which cations and anions are alternately arranged. In addition, vacancies for cations or anions may also be included.

In addition, in this specification and the like, the pseudo-spinel crystal structure of a composite oxide containing lithium and a transition metal means that the space group is R-3m; although it is not a spinel crystal structure, cobalt, magnesium Ions such as Oxygen occupy the six-coordination position of oxygen, and the arrangement of the ions has a symmetry similar to that of the spinel structure. In addition, sometimes light elements such as lithium in the pseudo-spinel crystal structure occupy the four-coordination position of oxygen, and the arrangement of ions at this time has a symmetry similar to that of the spinel type.

In addition, it can be said that the pseudo-spinel type crystal structure has a crystal structure similar to the CdCl ₂ type crystal structure although there is Li irregularly between layers. It is known that the above-mentioned crystal structure similar to the CdCl ₂ type crystal structure is similar to the crystal structure when lithium nickelate is charged to a charge depth of 0.94 (Li _0.06 NiO ₂ ), but the layered rock salt type containing a large amount of pure lithium cobaltate or cobalt A positive electrode active material generally does not have the above-mentioned crystal structure.

Layered rock-salt crystals and anions in rock-salt crystals form the cubic closest-packed structure (face-centered cubic lattice structure). It is speculated that the anions of pseudo-spinel crystals also have a cubic closest-packed structure. When layered rock-salt crystals are in contact with rock-salt crystals, there is a uniformly aligned crystal plane of the cubic closest packing structure formed by anions. The space group of layered rock-salt crystals and pseudo-spinel crystals is R-3m, which is the same as the space group of rock-salt crystals Fm-3m (the space group of general rock-salt crystals) and Fd-3m (with the simplest Symmetrical rock-salt-type crystals have different space groups), so the Miller indices of layered rock-salt-type crystals and pseudo-spinel-type crystals and rock-salt-type crystals satisfy the above conditions are different. In this specification, in the case of layered rock salt crystals, pseudo-spinel crystal structures, and rock salt crystals, the alignment of the cubic closest-packed structure composed of anions means that the crystal orientations are substantially identical.

It can be based on TEM (transmission electron microscope) image, STEM (scanning transmission electron microscope) image, HAADF-STEM (high angle annular dark field-scanning transmission electron microscope) image, ABF-STEM (annular bright field scanning Transmission electron microscope) image, etc., it is judged that the crystal orientations of the two regions are roughly consistent. In addition, X-ray diffraction (XRD), electron diffraction, neutron diffraction, and the like may be used as a basis for judgment. When the crystal orientations are substantially identical, the difference in the direction of the columns in which cations and anions are alternately arranged linearly can be observed in a TEM image or the like of 5 degrees or less, more preferably 2.5 degrees or less. Note that light elements such as oxygen and fluorine may not be clearly observed in TEM images, etc. In this case, the consistency of alignment can be judged from the arrangement of metal elements.

In addition, in this specification etc., the theoretical capacity of a positive electrode active material means the electric quantity when all the lithium ions contained in a positive electrode active material which can intercalate and desorb are desorbed. For example, the theoretical capacity of LiCoO ₂ is 274mAh/g, that of LiNiO ₂ is 274mAh/g, and that of LiMn ₂ O ₄ is 148mAh/g.

In addition, in this specification and the like, the depth of charge when all the lithium ions that can be intercalated and desorbed is 0, and the depth of charge when all the lithium ions that can be intercalated and desorbed contained in the positive electrode active material are desorbed is 1.

In addition, in this specification and the like, charging refers to moving lithium ions from the positive electrode to the negative electrode in the battery and moving electrons from the negative electrode to the positive electrode in the external circuit. Charging the positive electrode active material refers to detaching lithium ions. In addition, a positive electrode active material having a depth of charge exceeding 0.5 is called a charged positive electrode active material. In addition, a positive electrode active material having a depth of charge of 0.8 or more is referred to as a high voltage charged positive electrode active material. Thus, for example, LiCoO ₂ can be said to be a positive electrode active material charged at a high voltage if it is charged to 219.2 mAh/g or more. In addition, in lithium cobalt oxide with an impurity element of 5 at% or less (the impurity element refers to elements other than lithium, cobalt, and oxygen) in an environment of 25°C until the battery voltage reaches 4.6V (when the counter electrode is lithium). A positive electrode active material charged at a constant current and then charged at a constant voltage until the current value becomes 0.01C is also referred to as a positive electrode active material charged at a high voltage.

Likewise, discharging means moving lithium ions from the negative electrode to the positive electrode within the battery and moving electrons from the positive electrode to the negative electrode in the external circuit. The discharge of the positive electrode active material refers to the intercalation of lithium ions. In addition, a positive electrode active material having a depth of charge of 0.5 or less is referred to as a discharged positive electrode active material. In addition, a positive electrode active material with a depth of charge of 0.06 or less or a positive electrode active material that has been discharged to a capacity of 90% or more of the charge capacity from a high-voltage charged state is called a fully discharged positive electrode active material. For example, LiCoO ₂ has a charge capacity of 219.2mAh/g, which means that it has been charged at a high voltage, and the positive electrode active material after discharging 90% of the charge capacity of 197.3mAh/g or more from this state is fully discharged Positive active material. In addition, in lithium cobalt oxide with an impurity element of 5 at% or less (the impurity element refers to an element other than lithium, cobalt, and oxygen) in an environment of 25°C until the battery voltage becomes 3V or less (when the counter electrode is lithium). The positive active material after constant current discharge is also referred to as fully discharged positive active material.

Embodiment 1 [Structure of Positive Electrode Active Material] First, a positive electrode active material 100 according to one embodiment of the present invention and a conventional positive electrode active material will be described with reference to FIGS. 1 and 2 , and differences between the two will be described. Note that the conventional positive electrode active material described in this embodiment is pure lithium cobaltate (LiCoO ₂ ), in which no elements other than lithium, cobalt, and oxygen are added to the inside and no lithium, cobalt, and oxygen are coated on the surface layer. Elements other than cobalt and oxygen.

<Known positive electrode active material> Lithium cobaltate is mentioned as an example of a known positive electrode active material. As described in Non-Patent Document 2 and Non-Patent Document 3, the crystal structure of lithium cobaltate changes according to the depth of charge. Figure 2 shows a typical crystal structure of lithium cobaltate.

As shown in FIG. 2, LiCoO ₂ whose charge depth is 0 (discharged state) includes a region having a crystal structure of space group R-3m, including three CoO ₂ layers in a unit cell. Therefore, this crystal structure is sometimes referred to as an O3 type crystal structure. Note that the CoO ₂ layer refers to a structure in which an octahedral structure formed of cobalt and six coordinated oxygen maintains a shared ridge on one plane.

When the charge depth is 1, it has a crystal structure of space group P-3m1, and the unit cell includes one _CoO2 layer. Therefore, this crystal structure is sometimes referred to as an O1 type crystal structure.

When the depth of charge is around 0.88, LiCoO ₂ has a crystal structure of space group R-3m. It can also be said that this structure is a structure in which CoO ₂ structures such as P-3m1(O1) and LiCoO ₂ structures such as R-3m(O3) are alternately laminated. Therefore, this crystal structure is sometimes referred to as an H1-3 type crystal structure. Actually, the number of cobalt atoms per unit cell of the H1-3 crystal structure is twice that of other structures. However, in this specification such as FIG. 2 , the c-axis in the H1-3 type crystal structure is represented as 1/2 of the unit cell for easy comparison with other structures.

When charging and discharging at a high voltage with a depth of charge of about 0.88 or higher are repeated, the crystal structure of LiCoO2 repeatedly changes between the H1-3 type crystal structure and the R _- 3m(O3) structure in the discharged state.

However, the deviation of the _CoO2 layer of the above two crystal structures is large. As shown by dashed lines and arrows in Figure 2, in the H1-3 crystal structure, the _CoO2 layer deviates significantly from R-3m(O3). Such dynamic structural changes can adversely affect the stability of the crystalline structure.

Furthermore, the volume difference is also large. The details will be described in Example 1. When comparing the same number of cobalt atoms, the volume difference between the H1-3 type crystal structure and the O3 type crystal structure in the discharged state is 3.5% or more.

In addition to the above, the H1-3 type crystal structure has a high possibility of being unstable in a continuous structure of CoO ₂ layers like P-3m1(O1).

Accordingly, when high-voltage charge and discharge are repeated, the crystal structure of lithium cobalt oxide collapses. On the other hand, the collapse of the crystal structure causes deterioration of cycle characteristics. This is because the collapse of the crystalline structure reduces the number of places where lithium can stably exist, making it difficult to intercalate and deintercalate lithium.

<Positive electrode active material according to one embodiment of the present invention> <<Inside>> In contrast, the difference between the crystal structure and volume of the positive electrode active material 100 according to one embodiment of the present invention is smaller when it is fully discharged and when it is charged at a high voltage. small.

FIG. 1 shows the crystal structure of the positive electrode active material 100 before and after charging and discharging. The positive electrode active material 100 contains lithium, cobalt, and oxygen. Preferably, magnesium is contained in addition to the above. Moreover, it is preferable to contain halogens, such as fluorine and chlorine. In addition, it is preferable to contain at least one of titanium and aluminum.

The crystal structure of charge depth 0 (discharged state) in FIG. 1 is the same R-3m (O3) as in FIG. 2 . On the other hand, when the fully charged depth of charge is about 0.88, the positive electrode active material 100 according to one embodiment of the present invention has a crystal structure different from that in FIG. 2 . In this specification, the crystal structure of the above-mentioned space group R-3m is referred to as a pseudo-spinel crystal structure. In addition, in order to explain the symmetry of the cobalt atom and the symmetry of the oxygen atom, the representation of lithium is omitted in the pseudo _- spinel crystal structure shown in Fig. % of lithium. In addition, in both the O3 type crystal structure and the pseudo-spinel type crystal structure, it is preferable that a small amount of magnesium exists between _CoO2 layers, that is, at the lithium site. In addition, it is preferable that a small amount of halogen such as fluorine exists at the oxygen site. Furthermore, at least one of aluminum and titanium is preferably present in a small amount at the cobalt site.

Changes in the crystal structure when lithium is released from the positive electrode active material 100 are suppressed. For example, as shown by the dotted line in Fig. 1, there is almost no deviation of the _CoO2 layer in the above crystal structure.

In addition, the details will be described in Example 1. In the positive electrode active material 100, the volume difference per unit cell of the O3 type crystal structure with a charge depth of 0 and the pseudo spinel crystal structure with a charge depth of 0.88 is 2.5% or less, specifically 2.2% or less.

Therefore, even if charge and discharge are repeated at a high voltage, the crystal structure does not easily collapse.

The coordinates of cobalt and oxygen per unit cell in the pseudo-spinel crystal structure can be represented by Co(0,0,0.5), O(0,0,x) (0.20≤x≤0.25), respectively.

Magnesium present in a small amount between the CoO ₂ layers has an effect of suppressing deviation of the CoO ₂ layer. Thereby the pseudo-spinel type crystal structure is easily obtained when magnesium is present between the _CoO2 layers. Therefore, it is preferable that magnesium is also distributed inside the particles of the positive electrode active material 100 . In addition, in order to distribute the magnesium inside the particles, heat treatment is preferably performed during the process of manufacturing the positive electrode active material 100 .

However, when the temperature of the heat treatment is too high, cation mixing occurs and the possibility of magnesium intruding into the cobalt site increases. When magnesium is present at the cobalt site, it has no effect on maintaining R-3m. In addition, when the heat treatment temperature is too high, there is a possibility that adverse effects such as reduction of cobalt to bivalent and diffusion of lithium may occur.

Therefore, it is preferable to add a halogen compound such as a fluorine compound to lithium cobaltate before performing heat treatment for distributing magnesium in the particle. By adding a halogen compound, the melting point of lithium cobalt oxide is lowered. By lowering the melting point, magnesium can be easily distributed throughout the particles at a temperature at which cation mixing is unlikely to occur. When a fluorine compound is also present, it can be expected to improve the corrosion resistance against hydrofluoric acid generated by decomposition of the electrolytic solution.

When at least one of titanium and aluminum exists in a small amount at the cobalt site of the positive electrode active material 100, the change in the crystal structure can be further suppressed.

Magnesium distributed inside the positive electrode active material 100 has the effect of suppressing deviation of the CoO ₂ layer, but at the same time, cobalt around the magnesium is easily reduced to 2 in order to maintain charge balance. Therefore, when there is an excess of magnesium, a part of the particles of the positive electrode active material 100 may become a solid solution structure of MgO and CoO(II). In the structural region where MgO and CoO(II) are in solid solution, there is no path for insertion and removal of lithium.

However, titanium is the most stable at 4 valence, followed by 3 valence, and aluminum is stable at 3 valence. Both titanium and aluminum are unstable at 2 valence. Thus, titanium or aluminum present at the cobalt site is not easily reduced to divalent even if magnesium is present at the surrounding lithium site. Therefore, it is considered that when a small amount of titanium or aluminum exists at the cobalt site, it is difficult to form a solid solution structure of MgO and CoO(II).

In addition, when at least one of titanium and aluminum is included, oxygen is not easily released especially in a charged state. In other words, since the activity of oxygen bonded to titanium or aluminum decreases, thereby reducing the catalytic effect on oxidative decomposition of the electrolytic solution, oxidative decomposition of the electrolytic solution does not easily occur on the surface of the positive electrode active material.

<<Surface part>> Magnesium is preferably distributed throughout the entire particle of the positive electrode active material 100, but in addition, the magnesium concentration in the particle surface part is preferably higher than the average of the entire particle. It can be said that the particle surface is full of crystal defects, so it is a part that tends to be unstable and the crystal structure tends to change. When the concentration of magnesium in the surface layer is high, the change of the crystal structure can be suppressed more effectively. In addition, when the concentration of magnesium in the surface layer is high, it is expected that the corrosion resistance against hydrofluoric acid generated by decomposition of the electrolytic solution will be improved.

In addition, it is preferable that the concentration of fluorine in the surface layer portion of the positive electrode active material 100 is also higher than the average of the entire particle. The corrosion resistance to hydrofluoric acid can be effectively improved by the presence of fluorine in the surface layer portion of the region in contact with the electrolytic solution.

In addition, it is preferable that the concentration in the surface layer portion of either titanium or aluminum is also higher than the average of the entire particle. When a large amount of either titanium or aluminum exists in a region with a high magnesium concentration, the effect of suppressing changes in the CoO ₂ layer can be exhibited more strongly. In addition, oxidative decomposition of the electrolytic solution on the surface of the positive electrode active material is less likely to occur.

In this way, it is preferable that the concentration of at least one of magnesium, fluorine, titanium, and aluminum in the surface layer of the positive electrode active material 100 is higher than that in the inside, and to have a different composition from the inside. As this composition, it is preferable to adopt a crystal structure stable at normal temperature. Accordingly, the surface layer may have a different crystal structure from that of the inside. For example, at least a part of the surface portion of the positive electrode active material 100 may have a rock-salt crystal structure. Note that, when the surface layer has a different crystal structure from that of the inside, it is preferable that the orientation of crystals in the surface layer and the inside are substantially the same.

Note that when the positive electrode active material 100 contains magnesium and titanium, the peak of the titanium concentration is preferably present in a region deeper than the peak of the magnesium concentration. Since titanium may be tetravalent or trivalent, the distance between titanium and oxygen varies depending on the valence of titanium. Accordingly, even if the distance between the metal and oxygen is not uniform, the surroundings of the titanium atoms are easily stabilized. For example, when the surface layer of the positive electrode active material 100 has a rock-salt crystal structure, the region containing titanium serves as a buffer region and contributes to the stabilization of the internal crystal structure.

However, when there is only MgO in the surface layer or only MgO and CoO(II) have a solid solution structure, as described above, there is no path for insertion and extraction of lithium. Therefore, the surface layer needs to contain at least cobalt, and also contains lithium during discharge so as to have a path for insertion and release of lithium. In addition, the concentration of cobalt is preferably higher than that of magnesium.

<<Grain Boundary>> Magnesium, halogen, cobalt, aluminum, or titanium contained in the positive electrode active material 100 may exist irregularly and in a small amount inside, but it is preferable that a part thereof is segregated at the grain boundary.

In other words, the magnesium concentration of the crystal grain boundary and its vicinity of the positive electrode active material 100 is preferably higher than that of other inner regions. In addition, it is preferable that the fluorine concentration at the crystal grain boundary and its vicinity is also high. In addition, it is preferable that the concentration of one of titanium and aluminum in the crystal grain boundary and its vicinity is also high.

Like particle surfaces, crystal grain boundaries are also plane defects. Therefore, it becomes unstable easily and the crystal structure tends to start to change. Accordingly, when the magnesium concentration at the crystal grain boundary and its vicinity is high, the change of the crystal structure can be suppressed more effectively. In addition, when the concentration of any one of titanium and aluminum in the crystal grain boundary and its vicinity is high, the effect of suppressing the change of the CoO ₂ layer can be exerted strongly.

In addition, when the magnesium and fluorine concentrations in the crystal grain boundaries and their vicinity are high, even if cracks occur along the crystal grain boundaries of the particles of the positive electrode active material 100, the magnesium and fluorine concentrations near the surface caused by the cracks will change. high. Therefore, the corrosion resistance to hydrofluoric acid of the positive electrode active material after the cracks are formed can also be improved.

Note that in this specification and the like, the vicinity of a crystal grain boundary refers to a region within a range from the grain boundary to about 10 nm.

<<Particle Size>> When the particle size of the positive electrode active material 100 is too large, there are problems such as that the diffusion of lithium becomes difficult, and the surface of the active material layer is too rough when coated on the current collector. On the other hand, when the particle diameter of the positive electrode active material 100 is too small, there are problems such as difficulty in supporting the active material layer when coating on the current collector, and excessive reaction with the electrolytic solution. Therefore, D50 (also referred to as a median diameter) is preferably not less than 1 mm and not more than 100 mm, more preferably not less than 2 mm and not more than 40 mm.

<Analysis method> In order to determine whether a certain material is the positive electrode active material 100 of one embodiment of the present invention that shows a pseudo-spinel crystal structure when charged at a high voltage, the positive electrode charged at a high voltage can be borrowed Judgment is made by analysis using XRD, electron diffraction, neutron diffraction, electron spin resonance (ESR: Electron Spin Resonance), nuclear magnetic resonance (NMR), or the like. In particular, XRD is preferable because it has the following advantages: the crystal structure of the positive electrode active material can be analyzed with high resolution; the height of crystallinity and the alignment of the crystal can be compared; the periodicity of the crystal lattice can be analyzed Distortion and grain size; sufficient accuracy can be obtained also when directly measuring the positive electrode obtained by disassembling the secondary battery, etc.

As described above, the positive electrode active material 100 according to one embodiment of the present invention is characterized in that there is little change in the crystal structure between the high-voltage charge state and the discharge state. A material whose crystal structure varies greatly between high-voltage charge and discharge accounts for more than 50% is not preferable because it cannot withstand high-voltage charge and discharge. The details will be described in Example 1. Note that sometimes the desired crystal structure cannot be achieved only by adding elements. For example, lithium cobaltate containing magnesium and fluorine may have a pseudo-spinel crystal structure of more than 60 wt%, and may have a H1-3 crystal structure of more than 50%. In addition, when a predetermined voltage is used, the pseudo-spinel crystal structure becomes almost 100%, and when the predetermined voltage is further increased, an H1-3 crystal structure may occur. Therefore, when judging whether it is the positive electrode active material 100 according to one embodiment of the present invention, it is necessary to analyze the crystal structure such as XRD.

"Charging method" The high-voltage charging for the above judgment can be performed using, for example, a coin cell (CR2032 type, diameter 20 mm, height 3.2 mm) manufactured using lithium as a counter electrode.

More specifically, as the positive electrode, a mixture of positive active material, acetylene black (AB), and polyvinylidene fluoride (PVDF) in the ratio of positive active material: AB:PVDF=95:3:2 (weight ratio) can be used. The positive electrode is formed by coating the positive electrode current collector of the slurry on the aluminum foil.

Lithium metal can be used as a counter electrode. Note that when a material other than lithium metal is used as the counter electrode, the potential of the positive electrode is different from that of the secondary battery. For example, when focusing on the potential of the positive electrode, charging at 4.5 V for graphite as the counter electrode roughly corresponds to charging at 4.6 V for lithium as the counter electrode. Unless otherwise specified, the voltage and potential in this specification and the like refer to the potential of the positive electrode.

As an electrolyte contained in the electrolytic solution, 1 mol/L lithium hexafluorophosphate (LiPF ₆ ) was used. As the electrolytic solution, an electrolytic solution obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3:7 and 2 wt % vinylene carbonate (VC) can be used.

Polypropylene with a thickness of 25 mm can be used as the separator.

The positive electrode can and the negative electrode can may be formed of stainless steel (SUS).

The coin cell produced under the above conditions was charged at a constant current of 4.6V and 0.5C, and then the constant voltage charge was continued until the current value reached 0.01C. 1C was set here at 137 mA/g. The temperature was set to 25°C. A positive electrode active material charged at a high voltage can be obtained by disassembling the coin cell after charging as described above and taking out the positive electrode. In order to prevent the taken-out positive electrode active material from reacting with external components when various analyzes are performed thereafter, it is preferable to seal under an argon atmosphere. For example, XRD can be performed under conditions of a sealed container enclosed in an argon atmosphere.

<<XRD>> FIG. 3 shows an ideal powder XRD pattern represented by the CuKa1 line calculated from the models of the pseudo-spinel type crystal structure and the H1-3 type crystal structure. 3 also shows ideal XRD patterns calculated from the crystal structures of LiCoO ₂ (O3) with a charge depth of 0 and CoO ₂ (O1) with a charge depth of 1 for comparison. The patterns of LiCoO ₂ (O3) and CoO ₂ (O1) were obtained by using Reflex Powder Diffraction, one of the modules of Materials Studio (BIOVIA), from the crystal structure information obtained from ICSD (Inorganic Crystal Structure Database: Inorganic Crystal Structure Database). figured out. The range of 2q is set from 15° to 75°, Step size=0.01, wavelength l1 =1.540562´10 ^-10 m, l2 is not set, and Monochromator is set to single. The pattern of the H1-3 crystal structure was similarly calculated with reference to the crystal structure information described in Non-Patent Document 4. XRD pattern of pseudo-spinel crystal structure The crystal structure was estimated from the XRD pattern of the positive electrode active material according to one embodiment of the present invention using Rietveld analysis software TOPAS version 3 manufactured by Bruker AXS, and the XRD pattern was prepared in the same manner as others. Note that the XRD pattern of the cathode active material of one embodiment of the present invention is shown in Example 1.

As shown in Figure 3, in the pseudo-spinel crystal structure, the diffraction peaks are at 2q of 19.30±0.20° (above 19.10° and below 19.50°) and at 2q of 45.55±0.10° (above 45.45° and 45.65° below) appears. In more detail, sharp diffraction peaks appear at 2q of 19.30±0.10° (19.20° to 19.40°) and 2q of 45.55±0.05° (45.50° to 45.60°). However, the H1-3 type crystal structure and CoO ₂ (P-3m1, O1) do not have peaks at the above positions. From this, it can be said that the positive electrode active material 100 according to one embodiment of the present invention has peaks at 19.30±0.20° and 2q of 45.55±0.10° in a state charged with a high voltage.

Note that the positive electrode active material 100 according to one embodiment of the present invention has a pseudo-spinel crystal structure when charged at a high voltage, but it is not necessary that all particles have a pseudo-spinel crystal structure. It may have another crystal structure, and a part may be amorphous. Note that when the XRD pattern is subjected to Rietwald analysis, the pseudo-spinel crystal structure is preferably at least 50 wt%, more preferably at least 60 wt%, further preferably at least 66 wt%. When the pseudo-spinel crystal structure is 50 wt% or more, more preferably 60 wt% or more, and further preferably 66 wt% or more, a positive electrode active material with sufficiently excellent cycle characteristics can be realized.

In addition, the grain size of the pseudo-spinel crystal structure possessed by the particles of the positive electrode active material is only reduced to about 1/10 of that of LiCoO ₂ (O3) in the discharged state. Accordingly, even under the same XRD measurement conditions as those of the positive electrode before charging and discharging, a clear peak of the pseudo-spinel crystal structure was confirmed after high-voltage charging. _On the other hand, even if a part of pure LiCoO2 can have a structure similar to the pseudo-spinel type crystal structure, the crystal grain size becomes small, and its peak becomes broad and small. The grain size can be obtained from the half-width value of the XRD peak.

From the XRD pattern, characteristics about the internal structure of the positive electrode active material can be seen. In the positive electrode active material with a particle diameter (D50) of about 1 mm to 100 mm, the volume of the surface layer is very small compared with the inside, so even if the surface layer of the positive electrode active material 100 has a different crystal structure from the inside, it may be reflected in the XRD pattern. out of possibility.

<<ESR>> As shown in FIGS. 1 and 4A , in the positive electrode active material 100 having a pseudo-spinel crystal structure, cobalt exists at the oxygen hexa-coordinated position. As shown in Fig. 4B, in cobalt with oxygen hexa-coordination, the 3d orbital is split into e _g orbital and t _2g orbital, and the energy of the t _2g orbital arranged away from the direction where oxygen exists is low. Part of the cobalt existing at the position where the oxygen hexa is coordinated is diamagnetic Co ^{3 +} cobalt whose t _2g orbitals are all buried. Another part of the cobalt existing at the oxygen hexa-coordinated position may be paramagnetic Co ^{2 +} or Co ^{4 +} cobalt. The paramagnetic Co ^{2 +} or Co ^{4 +} cobalt includes one unpaired electron, so it cannot be judged by ESR, but either one of the valences can be adopted according to the valences of the surrounding elements.

On the other hand, it is described that some of conventional positive electrode active materials may have a spinel crystal structure in which lithium is not contained in the surface layer in a charged state. At this time, Co ₃ O ₄ has the spinel crystal structure shown in FIG. 5A .

When the spinel is represented by the general formula A[B ₂ ]O ₄ , the element A is four-coordinated to oxygen, and the element B is six-coordinated to oxygen. Therefore, in this specification and the like, the position where the oxygen four is coordinated is sometimes referred to as the A position, and the position where the oxygen hexa is coordinated is sometimes referred to as the B position.

In Co ₃ O ₄ having a spinel crystal structure, cobalt exists at the A site of oxygen tetracoordination in addition to the B site of oxygen hexacoordination. As shown in Figure 5B, in the splitting of oxygen tetracoordinated cobalt into e _g orbital and t _2g orbital, the energy of e _g orbital is low. Therefore, Co ^{2 +} , Co ^{3 +} and Co ^{4 +} with oxygen tetracoordination all include unpaired electrons and are paramagnetic. Therefore, when it is analyzed by ESR or the like that the particles sufficiently contain spinel-type Co ₃ O ₄ , the paramagnetic cobalt derived from Co ^{2 +} , Co ^{3 +} or Co ^{4 +} will definitely be detected in the oxygen four-coordination. peak.

However, in the positive electrode active material 100 according to one embodiment of the present invention, the peaks of the paramagnetic cobalt derived from the oxygen tetracoordination are too small to be confirmed. In other words, in the positive electrode active material according to one embodiment of the present invention, peaks derived from spinel-type Co ₃ O ₄ detected by ESR or the like may be small or unrecognizable in some cases, compared with conventional examples. Spinel-type Co ₃ O ₄ does not contribute to the charge-discharge reaction, and is unstable to heat, so the less spinel-type Co ₃ O ₄ the better. From this point of view, it can also be said that the positive electrode active material 100 is different from the conventional example.

《XPS》 X-ray photoelectron spectroscopy (XPS) can analyze the depth range from the surface to about 2 to 8nm (generally about 5nm), so it can quantitatively analyze the concentration of each element in about half of the surface layer. In addition, by performing narrow-scan analysis, the bonding state of elements can be analyzed. The measurement accuracy of XPS is about ±1 atomic % in many cases, although depending on the element, the lower detection limit is about 1 atomic %.

When XPS analysis of the positive electrode active material 100 is performed, the relative value of the magnesium concentration when the cobalt concentration is 1 is preferably 0.4 to 1.5, more preferably 0.45 to less than 1.00. In addition, the relative value of the fluorine concentration is preferably from 0.05 to 1.5, more preferably from 0.3 to 1.00. In addition, the relative value of the concentration of one of titanium and aluminum is preferably from 0.05 to 0.4, more preferably from 0.1 to 0.3.

In addition, when the positive electrode active material 100 is analyzed by XPS, the peak showing the bonding energy between fluorine and other elements is preferably 682 eV or more and less than 685 eV, more preferably about 684.3 eV. This value is different from both the bonding energy of LiF of 685 eV and the bonding energy of magnesium fluoride of 686 eV. In other words, when the positive electrode active material 100 contains fluorine, a bond other than lithium fluoride and magnesium fluoride is preferable.

In addition, when the XPS analysis of the positive electrode active material 100 is performed, the peak value showing the bonding energy between magnesium and other elements is preferably 1302 eV or more and less than 1304 eV, more preferably about 1303 eV. This value is different from the bonding energy of magnesium fluoride, which is 1305 eV, and is close to the bonding energy of MgO. In other words, when the positive electrode active material 100 contains magnesium, a bond other than magnesium fluoride is preferable.

"EDX" In EDX measurement, the method of measuring while scanning the inside of the area and performing two-dimensional evaluation of the area is sometimes called EDX surface analysis. In addition, the method of extracting the data of the linear region from the surface analysis of EDX and evaluating the atomic concentration distribution in the positive electrode active material particle may be called a line analysis.

By means of EDX surface analysis (such as element mapping), it is possible to quantitatively analyze the concentration of magnesium, fluorine, titanium or aluminum in the interior, surface and near the crystal grain boundary. In addition, by EDX-ray analysis, the concentration peaks of magnesium, fluorine, titanium, or aluminum can be analyzed.

When performing EDX analysis of the positive electrode active material 100, the concentration peak of magnesium in the surface layer is preferably present within the range of 3 nm from the surface of the positive electrode active material 100 to the center, more preferably within the range of 1 nm to the depth , and further preferably appear in the range to a depth of 0.5nm.

In addition, the fluorine distribution of the positive electrode active material 100 preferably overlaps with the magnesium distribution. Therefore, when performing EDX analysis, the peak concentration of fluorine in the surface layer is preferably present in the range from the surface of the positive electrode active material 100 to a depth of 3 nm toward the center, more preferably in a range of 1 nm in depth, and even more preferably To appear in the range to a depth of 0.5nm.

In addition, when performing EDX analysis, the peak of the concentration of at least one of titanium and aluminum in the surface layer of the positive electrode active material 100 is preferably present at a depth of 0.2 nm or more and 10 nm or less from the surface of the positive electrode active material 100 to the center. More preferably, it appears at a depth of not less than 0.5 nm and not more than 3 nm.

In addition, when performing line analysis or surface analysis of the positive electrode active material 100, the atomic number ratio (Mg/Co) of magnesium and cobalt near the crystal grain boundary is preferably 0.020 or more and 0.50 or less. More preferably, it is 0.025 or more and 0.30 or less. More preferably, it is 0.030 or more and 0.20 or less.

[Method for Manufacturing Positive Electrode Active Material] Next, an example of a method for manufacturing the positive electrode active material 100 according to one embodiment of the present invention will be described.

<Step S11: Preparation of starting materials> First, a lithium source and a cobalt source are prepared as starting materials. In addition, it is preferable to also prepare a magnesium source and a fluorine source as starting materials.

As the lithium source, for example, lithium carbonate and lithium fluoride can be used. As a cobalt source, for example, magnesium oxide can be used. As the magnesium source, for example, magnesium oxide, magnesium fluoride, magnesium hydroxide, lithium carbonate, etc. can be used. As a fluorine source, lithium fluoride, magnesium fluoride, etc. can be used, for example. In other words, lithium fluoride can be used as a lithium source as well as a fluorine source.

The atomic weight of magnesium contained in the magnesium source is preferably 0.001 to 0.1 when the atomic weight of cobalt is 1, more preferably 0.005 to 0.02, and still more preferably about 0.01.

The fluorine contained in the fluorine source is preferably 1.0 to 4 times the magnesium contained in the magnesium source (atomic ratio), more preferably 1.5 to 3 times.

<Step S12: Mixing of starting materials> Next, the above-mentioned starting materials are mixed. For mixing, for example, a ball mill, a sand mill, or the like can be used. When using a ball mill, for example, it is preferable to use zirconia balls as a medium.

<Step S13: First heat treatment> Next, the materials mixed in step S12 are heated. This step is sometimes called firing or first heat treatment. Heating is preferably carried out at 800°C or higher and lower than 1100°C, more preferably at 900°C or higher and 1000°C or lower, still more preferably at about 950°C. When the temperature is too low, there are concerns about decomposition of the starting material and insufficient melting. On the other hand, when the temperature is too high, there is a possibility that Co becomes a divalent defect due to reduction of Co, evaporation of Li, and the like.

The heating time is preferably not less than 2 hours and not more than 20 hours. Baking is preferably performed in an atmosphere such as dry air. Preferably, heating is carried out at 1000° C. for 10 hours, the heating rate is 200° C./h, and the flow rate of the drying atmosphere is 10 L/min. Then, the heated material was cooled to room temperature. For example, the cooling time from the holding temperature to room temperature is preferably not less than 10 hours and not more than 50 hours.

Lithium cobaltate can be synthesized by heating in step S13. When the starting material contains magnesium and fluorine, it becomes particles of a composite oxide in which magnesium and fluorine are distributed in lithium cobaltate.

In addition, as a starting material, previously synthesized composite oxide particles containing lithium, cobalt, fluorine, and magnesium can be used. In this case, step S12 and step S13 can be omitted. For example, lithium cobaltate particles (trade name: C-20F) manufactured by NIPPON CHEMICAL INDUSTRIAL CO., LTD. can be used as one of the starting materials. The particles are lithium cobaltate particles having a particle diameter of about 20 mm and containing fluorine, magnesium, calcium, sodium, silicon, sulfur, and phosphorus from the surface to a region that can be analyzed by XPS.

<Step S14: Covering with a material containing at least one of titanium and aluminum> Next, it is preferable to cover the surface of the lithium cobaltate particles with a material containing at least one of titanium and aluminum. As a coating method, a liquid phase method such as a sol-gel method, a solid phase method, a sputtering method, a vapor deposition method, a CVD (Chemical Vapor Deposition) method, a PLD (Pulsed Laser Deposition) method, or the like can be used. In the present embodiment, a case will be described in which a sol-gel method that can be expected to achieve uniform coverage and can be processed under atmospheric pressure is used.

First, dissolve titanium alkoxide, aluminum alkoxide or their mixture in alcohol, and then mix lithium cobaltate particles.

As the titanium alkoxide, for example, tetraisopropyl titanate (Titanium tetraisopropoxide: TTIP) can be used. As the aluminum alkoxide, for example, aluminum isopropoxide can be used. In addition, as the alcohol of the solvent, for example, isopropanol can be used.

Depending on the particle size of lithium cobaltate, the amount of metal alkoxide required varies. For example, when TTIP is used and the particle diameter (D50) of lithium cobaltate is about 20 mm, it is preferable to add 0.004 ml/g to 0.01 ml/g of TTIP to the particles of lithium cobaltate. When aluminum isopropoxide is used and the particles are the same, it is preferable to add aluminum isopropoxide of not less than 0.0279 g/g and not more than 0.0697 g/g to the particle diameter of lithium cobaltate.

Next, the liquid mixture of the alcoholic solution of the metal alkoxide and the lithium cobalt oxide was stirred in an atmosphere containing water vapor. For example, stirring can be performed using a magnetic stirrer. The stirring time may be sufficient as long as the hydrolysis and polycondensation reaction between water in the atmosphere and the metal alkoxide occurs, for example, it can be stirred at 25° C. for 4 hours at a humidity of 90% RH (Relative Humidity: Relative Humidity).

By reacting the water vapor in the atmosphere with the metal alkoxide, the sol-gel reaction can proceed more slowly than in the case of adding liquid water. In addition, by reacting the metal alkoxide and water at normal temperature, for example, the sol-gel reaction can proceed more slowly than heating at a temperature exceeding the boiling point of the solvent alcohol. By slowly carrying out the sol-gel reaction, a coating layer with uniform thickness and high quality can be formed.

The precipitate was collected from the mixed liquor after the above treatment. As a collection method, filtration, centrifugation, evaporation and drying and solidification, etc. can be used. The precipitate can be washed with the same alcohol as the solvent used to dissolve the metal alkoxide.

Next, the collected residue is dried. For example, a vacuum or ventilation drying treatment is performed at 70° C. for 1 hour or more and 4 hours or less.

<Step S15: Second heat treatment> Next, the particles of lithium cobalt oxide coated with a material containing titanium or aluminum produced in step S14 are heated. This step is sometimes called a second heat treatment.

During heating, the time to maintain the temperature is preferably from 1 hour to 50 hours, more preferably from 2 hours to 20 hours. When the heating time is too short, there is a possibility that the segregation in the surface layer part and the vicinity of the crystal grain boundary is insufficient when magnesium and fluorine are added. However, if the heating time is too long, the above-mentioned metals may diffuse excessively when covering with titanium or aluminum, thereby reducing the concentration in the surface layer and near the crystal grain boundaries.

The holding temperature is preferably from 500°C to 1200°C, more preferably from 700°C to 920°C, further preferably from 800°C to 900°C. When the temperature is kept too low, there is a concern that the segregation of magnesium may not occur. However, when the temperature is kept too high, there are also concerns that Mg is also distributed at the Co site, and Co ^{2 +} such as CoO is stabilized instead of Co ^{3 +} like LiCO ₂ , and the layered structure of CoO ₂ cannot be maintained.

The second heat treatment is preferably performed in an atmosphere containing oxygen. When the oxygen partial pressure is low, there is a concern that Co may be reduced unless the heating temperature is further lowered.

In this embodiment, the heating is performed under the following conditions: the holding temperature is 800° C.; the holding time is 2 hours; the heating rate is 200° C./h; the flow rate of oxygen is 10 L/min.

By setting the cooling time after heating long, it is easy to stabilize the crystal structure, which is preferable. For example, the cooling time from the holding temperature to room temperature is preferably not less than 10 hours and not more than 50 hours.

In this way, it is preferable to perform heating a plurality of times like the first heat treatment (step S13 ) and the second heat treatment (step S15 ). In the first heat treatment, heating is performed at a temperature higher than the melting point of Co ₃ O ₄ (895° C.) and the melting point of Li ₂ Co ₃ (723° C.) in order to sufficiently react the starting materials with each other. In the second heat treatment, heating is performed at a temperature lower than that of the first heat treatment in order to distribute magnesium between the _CoO2 layers. Specifically, the temperature at which Co ^{3 +} is more stable than Co ^{2 +} according to the Ellingham diagram is 920°C in the air, so the second heat treatment is preferably performed at 920°C or lower.

<Step S16: Collection> Next, the cooled particles are collected. Also, it is preferable to screen the particles. The cathode active material 100 according to one embodiment of the present invention can be manufactured through the above-mentioned manufacturing process.

In addition, after step S16, the covering by the sol-gel method from step S14 to step S16 may be repeated multiple times. The number of repetitions may be one or two or more. By repeating the sol-gel method and heat treatment, cracks can be reduced when cracks are generated in lithium cobaltate particles.

In addition, the types of metal alkoxides used when the sol-gel treatment is performed multiple times may be the same or different. When using different metal alkoxides, it is possible, for example, to use titanium alkoxides in the first sol-gel treatment and aluminum alkoxides in the second sol-gel treatment.

Note that in this embodiment, it is described that a material containing lithium, cobalt, and oxygen is used as the positive electrode active material 100 , but one embodiment of the present invention is not limited thereto. For example, the transition metal included in the positive electrode active material 100 is not limited to cobalt, and may include a very small amount of at least one of nickel and manganese. In addition, in addition to the above transition metals, a very small amount of aluminum may be added to the starting material.

In addition, in one embodiment of the present invention, it is sufficient as long as the change in the crystal structure of the positive electrode active material between when it is fully charged and when it is fully discharged can be suppressed. Therefore, it does not have to have the pseudo-spinel crystal structure defined in this specification, and does not need to contain elements such as magnesium, fluorine, titanium, or aluminum.

In addition, the positive electrode active material 100 may also contain carbon, sulfur, silicon, sodium, calcium, zirconium and other elements.

This embodiment mode can be used in combination with other embodiment modes as appropriate.

Embodiment 2 In this embodiment, examples of materials that can be used for a secondary battery including the positive electrode active material 100 described in the above embodiment will be described. In this embodiment, a secondary battery in which a positive electrode, a negative electrode, and an electrolytic solution are surrounded by an outer package will be described as an example.

[Positive electrode] The positive electrode includes a positive electrode active material layer and a positive electrode current collector.

á Positive electrode active material layer ñ The positive electrode active material layer contains at least a positive electrode active material. In addition, in addition to the positive electrode active material, the positive electrode active material layer may also include other substances such as a film on the surface of the active material, a conductive additive, or a binder.

As the positive electrode active material, the positive electrode active material 100 described in the above embodiment can be used. By using the positive electrode active material 100 described in the above embodiment, a secondary battery with high capacity and excellent cycle characteristics can be realized.

As the conductive additive, a carbon material, a metal material, a conductive ceramic material, or the like can be used. In addition, a fibrous material can also be used as a conductive additive. The proportion of the conductive additive in the total amount of the active material layer is preferably not less than 1 wt % and not more than 10 wt %, more preferably not less than 1 wt % and not more than 5 wt %.

By using a conductive additive, a conductive network can be formed in the active material layer. By using the conductive additive, the conductive path between positive electrode active materials can be maintained. An active material layer having high conductivity can be realized by adding a conductive additive to the active material layer.

As the conductive additive, for example, natural graphite, artificial graphite such as mesocarbon microspheres, carbon fiber, and the like can be used. As the carbon fibers, for example, carbon fibers such as mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers can be used. As carbon fibers, carbon nanofibers, carbon nanotubes, and the like can be used. For example, carbon nanotubes can be produced by a vapor phase growth method or the like. As the conductive additive, carbon materials such as carbon black (acetylene black (AB) and the like), graphite (black lead) particles, graphene, and fullerene can be used, for example. In addition, for example, metal powders or metal fibers of copper, nickel, aluminum, silver, gold, or the like, conductive ceramic materials, or the like can be used.

In addition, a graphene compound can also be used as a conductive additive.

Graphene compounds sometimes have excellent electrical properties such as high conductivity and excellent physical properties such as high flexibility and high mechanical strength. In addition, the graphene compound has a planar shape. Graphene compounds can form surface contacts with low contact resistance. Graphene compounds sometimes have very high conductivity even if they are thin, and thus can efficiently form conductive paths with a small amount in the active material layer. Therefore, since the contact area between the active material and the conductive additive can be increased by using the graphene compound as the conductive additive, it is preferable. Preferably, the graphene compound used as the conductive additive of the coating can be formed so as to cover the entire surface of the active material by using a spray drying device. In addition, since resistance can be reduced, it is preferable. It is particularly preferred here to use, for example, graphene, multilayer graphene or RGO (Reduced Graphene Oxide) as the graphene compound. Here, RGO refers to a compound obtained by reducing graphene oxide (graphene oxide: GO), for example.

When using an active material with a small particle size, for example, an active material with a particle size of 1 mm or less, the specific surface area of the active material is large, so more conductive paths connecting the active materials are required. Therefore, the amount of the conductive additive tends to increase, and the content of the active material tends to decrease relatively. When the content of the active material decreases, the capacity of the secondary battery also decreases. In this case, as the conductive additive, since it is not necessary to reduce the content of the active material, it is particularly preferable to use a graphene compound that can efficiently form a conductive path even in a small amount.

Hereinafter, an example of the cross-sectional structure of the active material layer 200 containing a graphene compound as a conductive additive will be described as an example.

FIG. 6A is a longitudinal cross-sectional view of the active material layer 200 . The active material layer 200 includes a granular positive electrode active material 100 , a graphene compound 201 serving as a conductive additive, and a binder (not shown). Here, as the graphene compound 201, for example, graphene or multilayer graphene can be used. In addition, the graphene compound 201 preferably has a sheet shape. The graphene compound 201 may form a sheet in which a plurality of multi-layer graphenes or (and) a plurality of single-layer graphenes are partially overlapped.

In the longitudinal section of the active material layer 200 , as shown in FIG. 6B , the sheet-shaped graphene compound 201 is dispersed substantially uniformly inside the active material layer 200 . In FIG. 6B , although the graphene compound 201 is schematically shown by a thick line, actually the graphene compound 201 is a thin film having the thickness of a single layer or multiple layers of carbon molecules. Since a plurality of graphene compounds 201 are formed in a manner covering a part of the plurality of granular positive electrode active materials 100 or in a manner attached to the surfaces of the plurality of granular positive electrode active materials 100, the graphene compounds 201 and the positive electrode active material 100 form surface contact.

Here, a network-shaped graphene compound sheet (hereinafter referred to as a graphene compound network or a graphene network) can be formed by combining a plurality of graphene compounds. When the graphene network covers the active material, the graphene network can be used as an adhesive to bind the compounds to each other. Therefore, the amount of binder can be reduced or no binder can be used, thereby increasing the volume of the electrode or the ratio of the active material to the weight of the electrode. That is, the capacity of the secondary battery can be increased.

Here, it is preferable to use graphene oxide as the graphene compound 201, mix the graphene oxide and an active material to form a layer to be the active material layer 200, and then reduce it. By using highly dispersible graphene oxide in a polar solvent in forming the graphene compound 201 , the graphene compound 201 can be dispersed substantially uniformly in the active material layer 200 . The solvent is volatilized and removed from the dispersion medium containing uniformly dispersed graphene oxide, and the graphene oxide is reduced, so that the graphene compounds 201 remaining in the active material layer 200 partially overlap each other and are dispersed in a manner of forming surface contact, Thereby, a three-dimensional conductive path can be formed. In addition, the reduction of graphene oxide can also be performed, for example, by heat treatment or using a reducing agent.

Therefore, unlike granular conductive additives such as acetylene black that form point contacts with active materials, graphene compound 201 can form surface contact with low contact resistance, so it is possible to improve the granular positive electrode with less graphene compound 201 than general conductive additives. Conductivity between the active material 100 and the graphene compound 201. Therefore, the ratio occupied by the positive electrode active material 100 in the active material layer 200 can be increased. Thereby, the discharge capacity of the secondary battery can be increased.

In addition, by using a spray drying device in advance, it is possible to form a graphene compound used as a conductive additive for the coating so as to cover the entire surface of the active material, and to form a conductive path between the active materials with the graphene compound.

As the binder, it is preferable to use, for example, styrene-butadiene rubber (SBR: styrene-butadiene rubber), styrene-isoprene-styrene rubber (styrene-isoprene-styrene rubber), acrylonitrile-butadiene rubber (acrylonitrile-isoprene-styrene rubber), butadiene rubber (butadiene rubber), ethylene-propylene-diene copolymer (ethylene-propylene-diene copolymer) and other rubber materials. Fluorocarbon rubber can also be used as a binder.

Moreover, it is preferable to use a water-soluble polymer as a binder, for example. As a water-soluble polymer, polysaccharide etc. can be used, for example. As polysaccharides, cellulose derivatives such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose, and regenerated cellulose, starch, and the like can be used. More preferably, these water-soluble polymers are used in combination with the aforementioned rubber material.

Alternatively, polystyrene, polymethyl acrylate, polymethyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide , polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN ), EPDM polymer, polyvinyl acetate, nitrocellulose and other materials.

As the binder, multiple types of the above-mentioned materials may also be used in combination.

For example, a material having a particularly high viscosity adjusting function and another material may be used in combination. For example, although a rubber material or the like has high cohesive force and high elasticity, it may be difficult to adjust the viscosity when mixed with a solvent. In such a case, for example, it is preferable to mix with a material whose viscosity adjusting function is particularly high. As a material having a particularly high viscosity adjusting function, for example, a water-soluble polymer can be used. In addition, the above-mentioned polysaccharides can be used as water-soluble polymers particularly excellent in viscosity adjustment function, for example, carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, and diethylcellulose can be used. Cellulose derivatives such as acyl cellulose and regenerated cellulose, and starch.

Note that cellulose derivatives such as carboxymethyl cellulose, for example, are converted into salts such as sodium salts and ammonium salts of carboxymethyl cellulose, so that their solubility is improved, and the effect as a viscosity modifier is easily exhibited. Due to the increased solubility, the dispersibility of the active material and other components can be improved when forming the electrode slurry. In this specification, cellulose and cellulose derivatives used as binders for electrodes include their salts.

By dissolving the water-soluble polymer in water to stabilize the viscosity, the active material and other materials combined as a binder, such as styrene butadiene rubber, can be stably dispersed in the aqueous solution. Since the water-soluble polymer has a functional group, it is expected to be easily and stably attached to the surface of the active material. Many cellulose derivatives, such as carboxymethylcellulose, have functional groups, such as a hydroxyl group and a carboxyl group, for example. Because of having functional groups, polymers are expected to interact and widely cover the surface of the active material.

When the binder covering or contacting the surface of the active material forms a film, it is also expected to be used as a passive film to exhibit the effect of suppressing the decomposition of the electrolyte solution. Here, the passive film is a film having no or very low conductivity, and for example, when the passive film is formed on the surface of the active material, it can suppress the decomposition of the electrolyte solution at the reaction potential of the battery. Even better, the passive film is capable of transporting lithium ions while suppressing electrical conductivity.

áPositive electrode current collector ñ As the positive electrode current collector, metals such as stainless steel, gold, platinum, aluminum, titanium, and their alloys can be used with highly conductive materials. In addition, the material used for the positive electrode current collector is preferably not dissolved by the potential of the positive electrode. In addition, an aluminum alloy to which an element improving heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, is added can also be used. Alternatively, metal elements that react with silicon to form silicides can also be used. Examples of metal elements that react with silicon to form silicides include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, and the like. The current collector may suitably have a foil shape, a plate shape (sheet shape), a mesh shape, a perforated metal mesh shape, an expanded metal mesh shape, or the like. The thickness of the current collector is preferably not less than 5 mm and not more than 30 mm.

[Negative electrode] The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also contain a conductive additive and a binder.

áNegative electrode active material ñ As the negative electrode active material, for example, alloy-based materials or carbon-based materials can be used.

As the negative electrode active material, an element capable of charge-discharge reaction by alloying/dealloying reaction with lithium can be used. For example, a material containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, and the like may be used. The capacity of this element is larger than that of carbon, especially the theoretical capacity of silicon is 4200mAh/g. Therefore, it is preferable to use silicon for the negative electrode active material. In addition, compounds containing these elements can also be used. Examples include SiO, Mg ₂ Si, Mg ₂ Ge, SnO, SnO ₂ , Mg ₂ Sn, SnS ₂ , V ₂ Sn ₃ , FeSn ₂ , CoSn ₂ , Ni ₃ Sn ₂ , Cu ₆ Sn ₅ , Ag ₃ Sn , Ag ₃ Sb, Ni ₂ MnSb, CeSb ₃ , LaSn ₃ , La ₃ Co ₂ Sn ₇ , CoSb ₃ , InSb and SbSn, etc. Elements capable of charging and discharging reactions through alloying/dealloying reactions with lithium, compounds containing the elements, and the like are sometimes referred to as alloy-based materials.

In this specification etc., SiO means silicon monoxide, for example. Alternatively, SiO can also be expressed as SiO _x . Here, x preferably represents a value near 1. For example, x is preferably from 0.2 to 1.5, more preferably from 0.3 to 1.2.

As the carbon-based material, graphite, easily graphitizable carbon (soft carbon), hardly graphitizable carbon (hard carbon), carbon nanotubes, graphene, carbon black, or the like can be used.

As graphite, artificial graphite, natural graphite, etc. are mentioned. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch-based artificial graphite, and the like. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB sometimes has a spherical shape and is therefore preferable. In addition, MCMB is easier to reduce its surface area, so it is sometimes preferred. As natural graphite, flaky graphite, spheroidized natural graphite, etc. are mentioned, for example.

When lithium ions are intercalated in graphite (when a lithium-graphite intercalation compound is formed), graphite shows a low potential (0.05 V to 0.3 V vs. Li/ Li ⁺ ) as low as that of lithium metal. Thus, the lithium ion secondary battery can show a high operating voltage. Graphite also has the following advantages: large capacity per unit volume; relatively small volume expansion; relatively cheap; and high safety compared with lithium metal, etc., so it is preferable.

In addition, as the negative electrode active material, oxides such as titanium dioxide (TiO ₂ ), lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ), lithium-graphite interlayer compound (Li _x C ₆ ), niobium pentoxide (Nb ₂ O ₅ ), tungsten oxide (WO ₂ ), molybdenum oxide (MoO ₂ ), etc.

In addition, as the negative electrode active material, Li _3-x M _x N (M=Co, Ni, Cu) having a Li ₃ N type structure containing lithium and a nitride of a transition metal can be used. For example, Li _2.6 Co _0.4 N ₃ is preferable because of its large charge and discharge capacity (900mAh/g, 1890mAh/cm ³ ).

When a nitride containing lithium and a transition metal is used as the negative electrode active material, lithium ions are contained in the negative electrode active material, so the negative electrode active material can be used in the same way as V ₂ O ₅ , Cr ₃ O ₈ , etc. used as the positive electrode active material. Combinations of materials containing lithium ions are therefore preferred. Note that when a material containing lithium ions is used as the positive electrode active material, a nitride containing lithium and a transition metal may also be used as the negative electrode active material by detaching lithium ions contained in the positive electrode active material in advance.

In addition, a material that causes a conversion reaction may also be used for the negative electrode active material. For example, a transition metal oxide that does not form an alloy with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), is used as the negative electrode active material. Examples of materials that cause conversion reactions include oxides such as Fe ₂ O ₃ , CuO, Cu ₂ O, RuO ₂ , and Cr ₂ O ₃ , sulfides such as CoS _0.89 , NiS, and CuS, Zn ₃ N ₂ , and Cu ₃ N, nitrides such as Ge ₃ N ₄ , phosphides such as NiP ₂ , FeP ₂ , and CoP ₃ , and fluorides such as FeF ₃ and BiF ₃ .

As the conductive additive and binder that can be contained in the negative electrode active material layer, the same materials as the conductive additive and binder that can be contained in the positive electrode active material layer can be used.

áNegative electrode collector ñ As the negative electrode collector, the same material as the positive electrode collector can be used. In addition, as the negative electrode current collector, it is preferable to use a material that does not alloy with carrier ions such as lithium.

[Electrolyte] The electrolyte contains a solvent and an electrolyte. As the solvent of the electrolytic solution, it is preferable to use an aprotic organic solvent, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, vinyl chloride carbonate, vinylene carbonate, g-butylene carbonate, etc. Lactone, g-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, Ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethyl ether (DME), dimethylsulfoxide, diethyl ether , methyl diglyme (methyl diglyme), acetonitrile, benzonitrile, tetrahydrofuran, cyclobutane, sultone, etc., or two or more of the above may be used in any combination and ratio.

In addition, by using one or more ionic liquids (room temperature molten salt) with flame retardancy and low volatility as the solvent of the electrolyte, even if the internal temperature of the secondary battery rises due to internal short circuit, overcharge, etc. The secondary battery is prevented from bursting, catching fire, and the like. Ionic liquids are composed of cations and anions, including organic cations and anions. Examples of organic cations used in the electrolytic solution include aliphatic onium cations such as quaternary ammonium cations, tertiary perjudium cations, and quaternary phosphonium cations, and aromatic cations such as imidazolium cations and pyridinium cations. In addition, examples of anions used in the electrolytic solution include monovalent amide-based anions, monovalent methide-based anions, fluorosulfonic acid anions, perfluoroalkylsulfonic acid anions, tetrafluoroboric acid anions, perfluoroalkylboronic acid anions, anion, hexafluorophosphate anion or perfluoroalkylphosphate anion, etc.

In addition, as the electrolyte dissolved in the above solvent, for example, LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiAlCl ₄ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC(CF ₃ SO ₂ ) ₃ , LiC(C ₂ F ₅ SO ₂ ) ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₄ F ₉ SO ₂ )(CF ₃ SO ₂ ), LiN(C ₂ F ₅ SO ₂ ) ₂ and other lithium salts, or two or more of them may be used in any combination and ratio.

As the electrolytic solution used in the secondary battery, it is preferable to use a highly purified electrolytic solution containing less granular dust and elements other than the constituent elements of the electrolytic solution (hereinafter, simply referred to as “impurities”). Specifically, the proportion of impurities in the weight of the electrolyte is less than 1%, preferably less than 0.1%, more preferably less than 0.01%.

In addition, vinylene carbonate, propane sultone (PS), tertiary butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bisoxalate borate (LiBOB) or Additives such as dinitrile compounds such as succinonitrile and adiponitrile. The concentration of the material to be added can be set to be, for example, 0.1 wt % or more and 5 wt % or less in the entire solvent.

In addition, a polymer gel electrolyte in which a polymer is swollen with an electrolytic solution can also be used.

In addition, safety against liquid leakage is improved by using polymer gel electrolyte. Furthermore, it is possible to reduce the thickness and weight of the secondary device.

As the gelled polymer, silicone gel, acrylic gel, acrylonitrile gel, polyethylene oxide gel, polypropylene oxide gel, fluoropolymer gel, etc. can be used.

As the polymer, for example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and the like, and copolymers containing these can be used. For example, PVDF-HFP which is a copolymer of PVDF and hexafluoropropylene (HFP) can be used. In addition, the formed polymer may also have a porous shape.

In addition, a solid electrolyte containing inorganic materials such as sulfides and oxides, and a solid electrolyte containing polymer materials such as PEO (polyethylene oxide) can be used instead of the electrolytic solution. When a solid electrolyte is used, no separator or spacer needs to be provided. In addition, since the entire battery can be solidified, there is no concern of liquid leakage, which significantly improves safety.

[Separator] In addition, the secondary battery preferably includes a separator. As the separator, for example, the following materials can be used: paper, non-woven fabric, glass fiber, ceramics, or synthetic fibers including nylon (polyamide), vinylon (polyvinyl alcohol-based fibers), polyester, acrylic resin, polyolefin, and polyurethane Wait. Preferably, the separator is processed into a bag shape and arranged to surround either the positive electrode or the negative electrode.

The separator may have a multilayer structure. For example, a ceramic-based material, a fluorine-based material, a polyamide-based material, or a mixture thereof may be applied to a thin film of an organic material such as polypropylene or polyethylene. As the ceramic material, for example, alumina particles, silicon oxide particles, and the like can be used. As a fluorine-based material, PVDF, polytetrafluoroethylene, etc. can be used, for example. As the polyamide-based material, for example, nylon, aramid (meta-aramid, para-aramid) or the like can be used.

Oxidation resistance can be improved by coating ceramic materials, thereby suppressing deterioration of the separator during high-voltage charging and discharging, thereby improving the reliability of the secondary battery. By coating the fluorine-based material, the separator and the electrodes can be easily brought into close contact, and output characteristics can be improved. Heat resistance can be improved by coating polyamide-based materials (especially aramid), thereby improving the safety of the secondary battery.

For example, a mixed material of alumina and aramid can be coated on both sides of a polypropylene film. Alternatively, a mixed material of alumina and aramid may be applied to the surface of the polypropylene film in contact with the positive electrode, and a fluorine-based material may be applied to the surface in contact with the negative electrode.

By adopting the separator of a multilayer structure, the safety of the secondary battery can be ensured even if the total thickness of the separator is small, and thus the capacity per unit volume of the secondary battery can be increased.

[External Package] As the external package contained in the secondary battery, for example, metal materials such as aluminum, resin materials, and the like can be used. In addition, a film-like outer package can also be used. As the film, for example, a film with a three-layer structure can be used: a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc. is provided with a flexible material such as aluminum, stainless steel, copper, nickel, etc. A metal thin film with excellent properties can also be provided on the metal thin film with an insulating synthetic resin film such as polyamide resin, polyester resin, etc. as the outer surface of the outer package.

[Charging and Discharging Method] The charging and discharging of the secondary battery can be performed, for example, as follows.

<<CC charging>> First, CC charging will be explained as one charging method. CC charging refers to a charging method in which a constant current flows through the secondary battery throughout the charging period, and charging is stopped when the voltage of the secondary battery reaches a predetermined voltage. As shown in FIG. 7A , the secondary battery is assumed to be an equivalent circuit of the internal resistance R and the capacity C of the secondary battery. In this case, the secondary battery voltage V _B is the sum of the voltage V R applied to the internal resistance _R and the voltage V _C applied to the capacity C of the secondary battery.

During CC charging, as shown in FIG. 7A , the switch is turned on, and a constant current I flows through the secondary battery. During this period, since the current I is constant, the voltage VR applied to the internal resistance _R is constant according to Ohm's law that VR = _R´I . On the other hand, the voltage V _C applied to the secondary battery capacity C rises with time. Therefore, secondary battery voltage V _B rises with time.

Then, charging is stopped when the secondary battery voltage V _B reaches a predetermined voltage, for example, 4.3V. When CC charging is stopped, as shown in FIG. 7B , the switch is turned off, and the current I=0. Therefore, the voltage VR applied to the internal resistance _R becomes 0V. Therefore, the drop in the secondary battery voltage V _B corresponds to the portion where the voltage of the internal resistor R no longer drops.

FIG. 7C shows examples of the secondary battery voltage V _B and charging current during CC charging and after CC charging is stopped. As can be seen from FIG. 7C , the secondary battery voltage V _B , which rose during the CC charging, slightly drops after the CC charging is stopped.

"CCCV Charging" Next, CCCV charging, which is a different charging method from the above, will be described. CCCV charging is a charging method that first performs CC charging to a predetermined voltage, and then performs CV (constant voltage) charging until the flowing current decreases, specifically, charging to a cut-off current value.

During CC charging, as shown in FIG. 8A , the constant current switch is turned on and the constant voltage switch is turned off, so that a constant current I flows through the secondary battery. During this period, since the current I is constant, the voltage VR applied to the internal resistance _R is constant according to Ohm's law that VR = _R´I . On the other hand, the voltage V _C applied to the secondary battery capacity C rises with time. Therefore, secondary battery voltage V _B rises with time.

Then, when the secondary battery voltage V _B reaches a predetermined voltage, for example, 4.3V, CC charging is switched to CV charging. During CV charging, as shown in FIG. 8B , the constant current switch is turned on and the constant voltage switch is turned off, so the secondary battery voltage V _B is kept constant. On the other hand, the voltage V _C applied to the secondary battery capacity C rises with time. Since V _B =V _R +V _C is satisfied, the voltage VR applied to the internal resistance _R becomes smaller with time. As the voltage VR applied to the internal resistance _R becomes smaller, the current I flowing through the secondary battery becomes smaller according to Ohm's law of VR= _R´I .

Then, when the current I flowing through the secondary battery becomes a predetermined current, for example, a current corresponding to 0.01C, charging is stopped. When the CCCV charging is stopped, as shown in FIG. 8C , all the switches are turned off, and the current I=0. Therefore, the voltage VR applied to the internal resistance _R becomes 0V. However, since the voltage VR applied to the internal resistor _R is sufficiently lowered by the CV charging, the secondary battery voltage _VB hardly drops even if the voltage of the internal resistor R does not drop any more.

FIG. 8D shows an example of the secondary battery voltage V _B and charging current during CCCV charging and after CCCV charging is stopped. As can be seen from FIG. 8D , the secondary battery voltage V _B hardly drops even after the CCCV charging is stopped.

<<CC Charge>> Next, CC discharge, which is one of the discharge methods, will be described. CC discharge refers to a discharge method in which a constant current is discharged from the secondary battery throughout the discharge period, and the discharge is stopped when the secondary battery voltage V _B reaches a predetermined voltage, for example, 2.5V.

FIG. 9 shows an example of the secondary battery voltage V _B and the discharge current during CC discharge. It can be seen from FIG. 9 that the secondary battery voltage V _B decreases as the discharge progresses.

Here, the discharge rate and the charge rate will be described. The discharge rate refers to the ratio of the current at the time of discharge to the battery capacity, and is represented by the unit C. In a battery with a rated capacity of X (Ah), the current equivalent to 1C is X (A). In the case of discharging with a current of 2X(A), it can be said that it is discharged at 2C, and in the case of discharging with a current of X/5(A), it can be said that it is discharged at 0.2C. In addition, the charging rate is also the same. When charging with a current of 2X (A), it can be said that it is charged at 2C, and when it is charged with a current of X/5 (A), it can be said that it is charged at 0.2C.

Embodiment 3 In this embodiment, an example of the shape of a secondary battery including the positive electrode active material 100 described in the above embodiment will be described. For materials used in the secondary battery described in this embodiment, the description in the above-mentioned embodiment can be referred to.

[Coin-Type Secondary Battery] First, an example of a coin-type secondary battery will be described. FIG. 10A is an external view of a coin-type (single-layer flat type) secondary battery, and FIG. 10B is a cross-sectional view thereof.

In the coin-type secondary battery 300 , a positive electrode can 301 serving as a positive terminal and a negative electrode can 302 serving as a negative terminal are insulated and sealed by a gasket 303 formed of polypropylene or the like. The positive electrode 304 is formed of a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact therewith. The negative electrode 307 is formed of a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact therewith.

Active material layers respectively included in the positive electrode 304 and the negative electrode 307 used in the coin-type secondary battery 300 may be formed on only one surface of the positive electrode and the negative electrode.

As the positive electrode can 301 and the negative electrode can 302 , metals such as nickel, aluminum, and titanium that are resistant to electrolytic solution, their alloys, or alloys of these and other metals (for example, stainless steel) can be used. In addition, in order to prevent corrosion caused by the electrolyte, the positive electrode can 301 and the negative electrode can 302 are preferably covered with nickel or aluminum. The positive electrode can 301 is electrically connected to the positive electrode 304 , and the negative electrode can 302 is electrically connected to the negative electrode 307 .

By impregnating these negative electrode 307, positive electrode 304, and separator 310 in the electrolyte, as shown in FIG. The positive electrode can 301 and the negative electrode can 302 are press-bonded with the gasket 303 to manufacture the coin-type secondary battery 300 .

By using the positive electrode active material described in the above embodiment for the positive electrode 304, the coin-type secondary battery 300 having a high capacity and excellent cycle characteristics can be realized.

Here, how the current flows when charging the secondary battery will be described with reference to FIG. 10C . When a secondary battery using lithium is viewed as a closed circuit, the direction in which lithium ions migrate is the same as the direction in which current flows. Note that in a secondary battery using lithium, since the anode and cathode, the oxidation reaction and the reduction reaction are switched according to charge or discharge, the electrode with a high reaction potential is called the positive electrode, and the electrode with the low reaction potential is called the negative electrode. Therefore, in this specification, even when charging, discharging, supplying reverse pulse current, and supplying charging current, the positive pole is called "positive pole" or "+ pole", and the negative pole is called "negative pole" or "- pole". ". If the terminology of anode and cathode related to oxidation reaction and reduction reaction is used, the anode and cathode during charging and discharging are reversed, which may cause confusion. Therefore, in this specification, the terms anode and cathode are not used. When the terms anode and cathode are used, it clearly indicates whether it is charging or discharging, and indicates whether it corresponds to the positive pole (+ pole) or the negative pole (- pole).

The two terminals shown in FIG. 10C are connected to a charger to charge the secondary battery 300 . As the charging of the secondary battery 300 progresses, the potential difference between the electrodes increases.

[Cylindrical Secondary Battery] Next, an example of a cylindrical secondary battery will be described with reference to FIGS. 11A to 11D . As shown in FIG. 11A , a cylindrical secondary battery 600 has a positive electrode cover (battery cover) 601 on the top surface, and a battery can (exterior can) 602 on the side and bottom surfaces. The positive electrode cap and the battery can (outer can) 602 are insulated by a gasket (insulating gasket) 610 .

FIG. 11B is a diagram schematically showing a cross section of a cylindrical secondary battery. Inside the hollow cylindrical battery can 602 is provided a battery element in which a strip-shaped positive electrode 604 and a strip-shaped negative electrode 606 are wound with a separator 605 interposed therebetween. Although not shown, the battery element is wound around the center pin. One end of the battery can 602 is closed and the other end is open. As the battery can 602 , metals such as nickel, aluminum, and titanium, alloys thereof, or alloys thereof with other metals (for example, stainless steel) that are corrosion-resistant to electrolytic solutions can be used. In addition, in order to prevent corrosion caused by the electrolyte, the battery can 602 is preferably covered with nickel or aluminum. Inside the battery can 602 , a battery element in which a positive electrode, a negative electrode, and a separator are wound is sandwiched between a pair of opposing insulating plates 608 and 609 . In addition, a non-aqueous electrolytic solution (not shown) is injected into the interior of the battery can 602 in which the battery elements are installed. As the non-aqueous electrolytic solution, the same electrolytic solution as that of the coin-type secondary battery can be used.

Since the positive electrode and the negative electrode used in the cylindrical secondary battery are wound, the active material is preferably formed on both surfaces of the current collector. The positive electrode 604 is connected to a positive electrode terminal (positive electrode current collecting lead) 603 , and the negative electrode 606 is connected to a negative electrode terminal (negative electrode current collecting lead) 607 . Metal materials such as aluminum can be used for both the positive terminal 603 and the negative terminal 607 . The positive terminal 603 is resistance welded to the safety valve mechanism 612 and the negative terminal 607 is resistance welded to the bottom of the battery can 602 . The safety valve mechanism 612 is electrically connected to the positive electrode cover 601 through a PTC (Positive Temperature Coefficient: positive temperature coefficient) element 611 . When the internal pressure of the battery rises above a predetermined critical value, the safety valve mechanism 612 cuts off the electrical connection between the positive electrode cap 601 and the positive electrode 604 . In addition, the PTC element 611 is a heat-sensitive resistance element whose resistance increases when the temperature rises, and the increase in resistance limits the amount of current to prevent abnormal heating. As the PTC element, barium titanate (BaTiO ₃ )-based semiconductor ceramics or the like can be used.

In addition, as shown in FIG. 11C , a plurality of secondary batteries 600 may be sandwiched between a conductive plate 613 and a conductive plate 614 to form a module 615 . The plurality of secondary batteries 600 may be connected in parallel, connected in series, or connected in parallel and then connected in series. By constituting the module 615 including a plurality of secondary batteries 600, large electric power can be extracted.

FIG. 11D is a top view of module 615 . For clarity, the conductive plate 613 is shown in dashed lines. As shown in FIG. 11D , the module 615 may include wires 616 to electrically connect the plurality of secondary batteries 600 . A conductive plate may be provided on the wire 616 in such a manner as to overlap the wire 616 . In addition, a temperature control device 617 may be provided between the plurality of secondary batteries 600 . When the secondary battery 600 is overheated, it can be cooled by the temperature control device 617 , and when the secondary battery 600 is too cold, it can be heated by the temperature control device 617 . Therefore, the performance of the module 615 is not easily affected by the external air temperature. The heat medium included in the temperature control device 617 is preferably insulating and non-combustible.

By using the positive electrode active material described in the above embodiment for the positive electrode 604, the cylindrical secondary battery 600 having a high capacity and excellent cycle characteristics can be realized.

[Structural Example of Secondary Battery] Another structural example of the secondary battery will be described with reference to FIGS. 12A to 16C .

12A and 12B are external views of a secondary battery. The secondary battery 913 is connected to the antenna 914 and the antenna 915 through the circuit board 900 . A label 910 is attached to the secondary battery 913 . Furthermore, as shown in FIG. 12B , the secondary battery 913 is connected to a terminal 951 and a terminal 952 .

The circuit board 900 includes terminals 911 and circuits 912 . The terminal 911 is connected to the terminal 951 , the terminal 952 , the antenna 914 , the antenna 915 , and the circuit 912 . In addition, a plurality of terminals 911 may be provided, and each of the plurality of terminals 911 may be used as a control signal input terminal, a power supply terminal, or the like.

The circuit 912 may also be provided on the back surface of the circuit substrate 900 . In addition, the shape of the antenna 914 and the antenna 915 is not limited to a coil shape, and may be, for example, a wire shape or a plate shape. In addition, antennas such as planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, or dielectric antennas can also be used. Alternatively, the antenna 914 or the antenna 915 may also be a flat conductor. This flat conductor can also be used as one of conductors for electric field coupling. In other words, the antenna 914 or the antenna 915 may also be used as one of the two conductors that the capacitor has. Thus, not only electromagnetic and magnetic fields but also electric fields can be used to exchange electric power.

The line width of the antenna 914 is preferably greater than the line width of the antenna 915 . Thus, the amount of electric power received by the antenna 914 can be increased.

The secondary battery includes a layer 916 between the antenna 914 and the antenna 915 and the secondary battery 913 . The layer 916 has, for example, a function of shielding the electromagnetic field from the secondary battery 913 . As the layer 916, for example, a magnetic substance can be used.

The structure of the secondary battery is not limited to the structures shown in FIGS. 12A and 12B .

For example, as shown in FIGS. 13A1 and 13A2 , antennas may be respectively provided on a pair of opposing surfaces of the secondary battery 913 shown in FIGS. 12A and 12B . FIG. 13A1 is an external view showing one side of the pair of surfaces, and FIG. 13A2 is an external view showing the other side of the pair of surfaces. In addition, the description of the secondary battery shown in FIG. 12A and FIG. 12B can be appropriately used for the same parts as those of the secondary battery shown in FIG. 12A and FIG. 12B .

As shown in FIG. 13A1 , an antenna 914 is provided on one of a pair of surfaces of a secondary battery 913 with a layer 916 interposed therebetween, and on the other of a pair of surfaces of a secondary battery 913 as shown in FIG. 13A2 . The sandwich layer 917 is provided with an antenna 918 . The layer 917 has, for example, a function of shielding the electromagnetic field from the secondary battery 913 . As the layer 917, for example, a magnetic substance can be used.

By adopting the above structure, it is possible to increase the size of both the antenna 914 and the antenna 918 . The antenna 918 has, for example, the function of performing data communication with external devices. As the antenna 918, for example, an antenna having a shape applicable to the antenna 914 can be used. As a communication method between the secondary battery and other devices using the antenna 918, a response method that can be used between the secondary battery and other devices, such as NFC (Near Field Communication), can be used.

Alternatively, as shown in FIG. 13B1 , a display device 920 may be provided on the secondary battery 913 shown in FIGS. 12A and 12B . The display device 920 is electrically connected to the terminal 911 . In addition, the label 910 may not be attached to the portion where the display device 920 is installed. In addition, the description of the secondary battery shown in FIG. 12A and FIG. 12B can be appropriately used for the same parts as those of the secondary battery shown in FIG. 12A and FIG. 12B .

On the display device 920 , for example, a video showing whether charging is in progress, a video showing the storage amount, or the like can be displayed. As the display device 920 , for example, electronic paper, a liquid crystal display device, an electroluminescent (also referred to as EL) display device, or the like can be used. For example, the power consumption of the display device 920 can be reduced by using electronic paper.

Alternatively, as shown in FIG. 13B2 , a sensor 921 may also be provided in the secondary battery 913 shown in FIGS. 12A and 12B . The sensor 921 is electrically connected to the terminal 911 through the terminal 922 . In addition, the description of the secondary battery shown in FIGS. 12A and 12B can be appropriately referred to for the same parts as those of the secondary battery shown in FIGS. 12A and 12B .

The sensor 921, for example, can have the function of measuring the following factors: displacement, position, speed, acceleration, angular velocity, rotation speed, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage , electricity, radiation, flow, humidity, slope, vibration, odor or infrared. By providing the sensor 921 , for example, data showing the environment in which the secondary battery is installed (temperature, etc.) can be detected and stored in the memory in the circuit 912 .

Furthermore, a configuration example of the secondary battery 913 will be described with reference to FIGS. 14A and 14B and FIG. 15 .

A secondary battery 913 shown in FIG. 14A includes a wound body 950 provided with a terminal 951 and a terminal 952 inside a case 930 . The jelly roll 950 is impregnated in the electrolytic solution inside the case 930 . The terminal 952 is in contact with the housing 930 , and the terminal 951 is not in contact with the housing 930 due to an insulating material or the like. Note that, for convenience, the housing 930 is shown separately in FIG. 14A , but the wound body 950 is actually covered by the housing 930 , and the terminals 951 and 952 extend outside the housing 930 . As the case 930, a metal material (for example, aluminum, etc.) or a resin material can be used.

In addition, as shown in FIG. 14B, multiple materials may also be used to form the housing 930 shown in FIG. 14A. For example, in the secondary battery 913 shown in FIG. 14B , the casing 930a and the casing 930b are bonded together, and the wound body 950 is provided in the area surrounded by the casing 930a and the casing 930b.

As the case 930a, an insulating material such as organic resin can be used. In particular, by using a material such as an organic resin for the surface forming the antenna, electric field shielding by the secondary battery 913 can be suppressed. In addition, if the electric field shielding by the case 930a is small, an antenna such as the antenna 914 or the antenna 915 may be provided inside the case 930a. As the case 930b, for example, a metal material can be used.

Furthermore, FIG. 15 shows the structure of the wound body 950 . The wound body 950 includes a negative electrode 931 , a positive electrode 932 and a separator 933 . The wound body 950 is formed by overlapping the negative electrode 931 and the positive electrode 932 to form a laminated sheet with the separator 933 interposed therebetween, and winding the laminated sheet. In addition, a plurality of laminations of the negative electrode 931 , the positive electrode 932 , and the separator 933 may be further stacked.

The negative electrode 931 is connected to the terminal 911 shown in FIGS. 12A and 12B via one of the terminal 951 and the terminal 952 . The positive electrode 932 is connected to the terminal 911 shown in FIGS. 12A and 12B via the other of the terminal 951 and the terminal 952 .

By using the positive electrode active material described in the above embodiment for the positive electrode 932, a secondary battery 913 having a high capacity and excellent cycle characteristics can be realized.

[Laminated Secondary Battery] Next, an example of a laminated secondary battery will be described with reference to FIGS. 16A to 22B . When the flexible laminated secondary battery is mounted on at least a partially flexible electronic device, the secondary battery can be bent along the deformation of the electronic device.

The laminated secondary battery 980 will be described with reference to FIGS. 16A to 16C . A laminated secondary battery 980 includes a jellyroll 993 shown in FIG. 16A . The wound body 993 includes a negative electrode 994 , a positive electrode 995 , and a separator 996 . Like the wound body 950 described in FIG. 15 , the wound body 993 is formed by stacking the negative electrode 994 and the positive electrode 995 with the separator 996 interposed therebetween to form a laminated sheet, and winding the laminated sheet.

In addition, the number of laminated layers composed of the negative electrode 994, the positive electrode 995, and the separator 996 can be appropriately designed according to the required capacity and device volume. The negative electrode 994 is connected to the negative electrode collector (not shown) by one of the lead electrode 997 and the lead electrode 998, and the positive electrode 995 is connected to the positive electrode collector (not shown) by the other of the lead electrode 997 and the lead electrode 998. .

As shown in FIG. 16B , the roll body 993 described above can be accommodated in a space formed by bonding a film 981 to be an outer package and a film 982 having a recessed portion by thermocompression bonding or the like, thereby manufacturing the roll body 993 shown in FIG. 16C . Secondary battery 980. The wound body 993 includes a lead electrode 997 and a lead electrode 998 , and the space formed by the film 981 and the film 982 having recesses is impregnated with an electrolytic solution.

The thin film 981 and the thin film 982 having recesses are made of, for example, a metal material such as aluminum or a resin material. When a resin material is used for the film 981 and the film with recesses 982, when a force is applied from the outside, the film 981 and the film with recesses 982 can be deformed, and a flexible secondary battery can be manufactured.

16B and 16C show an example using two films, but one film may be bent to form a space, and the above-mentioned wound body 993 may be accommodated in the space.

By using the positive electrode active material described in the above embodiment for the positive electrode 995, a secondary battery 980 having a high capacity and excellent cycle characteristics can be realized.

16A to 16C show an example of a secondary battery 980 in which a wound body is included in a space formed by a film that becomes an outer package, but it is also possible to use a secondary battery 980 that becomes an outer package as shown in FIGS. 17A and 17B. The space formed by the film of the packaging body includes a plurality of rectangular positive electrodes, separators, and negative electrodes of the secondary battery.

The laminated secondary battery 500 shown in Figure 17A includes: a positive electrode 503 comprising a positive electrode current collector 501 and a positive electrode active material layer 502; a negative electrode 506 comprising a negative electrode current collector 504 and a negative electrode active material layer 505; a separator 507; an electrolyte 508; and an outer packaging body 509. A separator 507 is provided between the positive electrode 503 and the negative electrode 506 provided in the outer package 509 . In addition, the electrolyte solution 508 is filled in the outer package 509 . As the electrolytic solution 508, the electrolytic solution described in Embodiment 2 can be used.

In the laminated secondary battery 500 shown in FIG. 17A , the positive electrode current collector 501 and the negative electrode current collector 504 also serve as terminals for electrical contact with the outside. Therefore, it may be arranged such that a part of the positive electrode current collector 501 and the negative electrode current collector 504 is exposed to the outside of the outer package 509 . In addition, the lead electrode and the positive electrode current collector 501 or the negative electrode current collector 504 are ultrasonically welded using a lead electrode to expose the lead electrode to the outside of the outer packaging body 509 without exposing the positive electrode current collector 501 and the negative electrode current collector 504 to the outside. The outside of the packaging body 509.

In the laminated secondary battery 500, as the outer package 509, for example, a film having a three-layer structure can be used: a film made of polyethylene, polypropylene, polycarbonate, ionomer, polyamide, etc. A highly flexible metal film such as aluminum, stainless steel, copper, nickel, etc. is provided on the film, and an insulating synthetic resin film such as polyamide resin, polyester resin, etc. is provided on the metal film as the outer surface of the outer package .

In addition, FIG. 17B shows an example of a cross-sectional structure of a laminated secondary battery 500 . For simplicity, Fig. 17A shows an example including two current collectors, but actually the battery includes multiple electrode layers as shown in Fig. 17B.

An example in Figure 17B includes 16 electrode layers. In addition, the secondary battery 500 has flexibility even including 16 electrode layers. FIG. 17B shows a structure of 16 layers in total with 8 layers of negative electrode current collector 504 and 8 layers of positive electrode current collector 501 . In addition, FIG. 17B shows a cross section of the extraction part of the negative electrode, and the eight-layer negative electrode current collector 504 is ultrasonically welded. Of course, the number of electrode layers is not limited to 16, and can be more than 16 or less than 16. When the number of electrode layers is large, a secondary battery having a larger capacity can be manufactured. In addition, when the number of electrode layers is small, it is possible to manufacture a thinner secondary battery having excellent flexibility.

Here, FIGS. 18 and 19 show an example of an external view of a laminated secondary battery 500 . In FIG. 18 and FIG. 19 , it includes: positive electrode 503 ; negative electrode 506 ; separator 507 ; outer packaging body 509 ; positive lead electrode 510 ; and negative lead electrode 511 .

FIG. 20A shows an external view of the positive electrode 503 and the negative electrode 506 . The positive electrode 503 includes a positive electrode current collector 501 , and a positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501 . In addition, the positive electrode 503 has a region where a part of the positive electrode current collector 501 is exposed (hereinafter referred to as a tab region (tab region)). The negative electrode 506 has a negative electrode current collector 504 , and the negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504 . In addition, the negative electrode 506 has a region where a part of the negative electrode current collector 504 is exposed, that is, a tab region. The area and shape of the tab regions of the positive and negative electrodes are not limited to the example shown in FIG. 20A .

[Method of Manufacturing Laminated Secondary Battery] Here, an example of a method of manufacturing a laminated secondary battery whose appearance is shown in FIG. 18 will be described with reference to FIGS. 20B and 20C .

First, the negative electrode 506, the separator 507, and the positive electrode 503 are laminated. FIG. 20B shows the stacked negative electrode 506 , separator 507 and positive electrode 503 . Here, an example using five sets of negative electrodes and four sets of positive electrodes is shown. Next, the tab regions of the positive electrodes 503 are bonded to each other, and the positive electrode lead electrode 510 is bonded to the tab region of the outermost positive electrode. As joining, ultrasonic welding etc. can be utilized, for example. Similarly, the tab regions of the negative electrodes 506 are bonded to each other, and the negative electrode lead electrode 511 is bonded to the tab region of the outermost negative electrode.

Next, the negative electrode 506 , the separator 507 , and the positive electrode 503 are placed on the outer package 509 .

Next, as shown in FIG. 20C , the exterior body 509 is folded along the portion indicated by the dotted line. Then, the outer peripheral portion of the outer package 509 is joined. As bonding, for example, thermocompression bonding or the like can be used. At this time, in order to inject the electrolytic solution 508 later, a region (hereinafter, referred to as an introduction port) that is not in contact with a part (or one side) of the exterior body 509 is provided.

Next, an electrolytic solution 508 (not shown) is introduced into the inside of the outer packaging body 509 from an inlet provided in the outer packaging body 509 . Preferably, the electrolyte solution 508 is introduced under a reduced pressure atmosphere or an inert gas atmosphere. Finally, the inlet is joined. In this way, the laminated secondary battery 500 can be manufactured.

By using the positive electrode active material described in the above embodiment for the positive electrode 503, the secondary battery 500 having a high capacity and excellent cycle characteristics can be realized.

[Bendable Secondary Battery] Next, an example of a bendable secondary battery will be described with reference to FIGS. 21A , 21B1 and 21B2 , 21C and 21D , and 22A and 22B .

FIG. 21A shows a schematic top view of a bendable secondary battery 250 . FIG. 21B1 , FIG. 21B2 , and FIG. 21C are schematic cross-sectional views along the truncation line C1 - C2 , the truncation line C3 - C4 , and the truncation line A1 - A2 in FIG. 21A . The secondary battery 250 includes an outer package 251 , and a positive electrode 211 a and a negative electrode 211 b accommodated inside the outer package 251 . The wire 212 a electrically connected to the positive electrode 211 a and the wire 212 b electrically connected to the negative electrode 211 b extend outside the outer packaging body 251 . In addition, an electrolytic solution (not shown) is sealed in the region surrounded by the outer package 251 in addition to the positive electrode 211 a and the negative electrode 211 b.

The positive electrode 211 a and the negative electrode 211 b included in the secondary battery 250 will be described with reference to FIGS. 22A and 22B . FIG. 22A is a perspective view illustrating the stacking order of the positive electrode 211 a , the negative electrode 211 b , and the separator 214 . FIG. 22B is a perspective view showing a lead wire 212a and a lead wire 212b in addition to the positive electrode 211a and the negative electrode 211b.

As shown in FIG. 22A , the secondary battery 250 includes a plurality of rectangular positive electrodes 211 a, a plurality of rectangular negative electrodes 211 b, and a plurality of separators 214 . The positive electrode 211a and the negative electrode 211b respectively include a protruding tab portion and a portion other than the tab. A positive electrode active material layer is formed on one surface of the positive electrode 211 a other than the tab, and a negative electrode active material layer is formed on one surface of the negative electrode 211 b other than the tab.

The positive electrode 211a and the negative electrode 211b are laminated so that the faces of the positive electrode 211a on which the positive electrode active material layer is not formed are in contact with each other, and the faces of the negative electrode 211b on which the negative electrode active material layer is not formed are in contact with each other.

In addition, a separator 214 is provided between the surface of the positive electrode 211 a on which the positive electrode active material layer is formed and the surface of the negative electrode 211 b on which the negative electrode active material layer is formed. For convenience, the spacer 214 is indicated by a dotted line in FIGS. 22A and 22B .

As shown in FIG. 22B , the plurality of positive electrodes 211a are electrically connected to the lead wire 212a in the joint portion 215a. In addition, the plurality of negative electrodes 211b are electrically connected to the lead wire 212b at the bonding portion 215b.

Next, the outer package 251 will be described with reference to FIGS. 21B1 , 21B2 , 21C, and 21D.

The outer package 251 has a film shape and is folded in half so as to sandwich the positive electrode 211a and the negative electrode 211b. The outer packaging body 251 includes a folded portion 261 , a pair of sealing portions 262 and a sealing portion 263 . The pair of sealing parts 262 are provided so as to sandwich the positive electrode 211a and the negative electrode 211b, and may also be referred to as side seals. In addition, the sealing portion 263 includes a portion overlapping the wires 212a and 212b and may also be referred to as a top seal.

The outer package 251 preferably has a wave shape in which ridges 271 and valleys 272 are alternately arranged in portions overlapping the positive electrode 211 a and the negative electrode 211 b. In addition, the sealing portion 262 and the sealing portion 263 of the outer package 251 are preferably flat.

FIG. 21B1 is a section cut off at a portion overlapping the ridge line 271 , and FIG. 21B2 is a cross section cut off at a portion overlapping the valley bottom line 272 . 21B1 and 21B2 both correspond to cross sections in the width direction of the secondary battery 250 and the positive electrode 211 a and the negative electrode 211 b.

Here, the end portions of the positive electrode 211 a and the negative electrode 211 b in the width direction, that is, the distance between the end portions of the positive electrode 211 a and the negative electrode 211 b and the sealing portion 262 is the distance La. When the secondary battery 250 is deformed by bending or the like, the positive electrode 211 a and the negative electrode 211 b are deformed so as to deviate from each other in the longitudinal direction as will be described later. At this time, if the distance La is too short, the outer package 251 may rub against the positive electrode 211a and the negative electrode 211b strongly, and the outer package 251 may be damaged. In particular, when the metal thin film of the exterior body 251 is exposed, the metal thin film may be corroded by the electrolytic solution. Therefore, it is preferable to set the distance La as long as possible. On the other hand, if the distance La is too long, the volume of the secondary battery 250 will increase.

In addition, preferably, the greater the total thickness of the laminated positive electrode 211 a and negative electrode 211 b is, the longer the distance La between the positive electrode 211 a and negative electrode 211 b and the sealing portion 262 is.

More specifically, when the total thickness of the laminated positive electrode 211a, negative electrode 211b, and separator 214 (not shown) is the thickness t, the distance La is not less than 0.8 times and not more than 3.0 times the thickness t, preferably not less than 0.9 times and not more than 3.0 times. 2.5 times or less, more preferably 1.0 times or more and 2.0 times or less. By setting the distance La within the above range, it is possible to realize a battery that is compact and highly reliable against bending.

In addition, when the distance between the pair of sealing portions 262 is the distance Lb, it is preferable that the distance Lb is sufficiently larger than the width of the positive electrode 211a and the negative electrode 211b (here, the width Wb of the negative electrode 211b). Thus, when the secondary battery 250 is repeatedly deformed by bending or the like, even if the positive electrode 211a and the negative electrode 211b are in contact with the outer package 251, a part of the positive electrode 211a and the negative electrode 211b can be shifted in the width direction, so that the positive electrode 211a can be effectively prevented from being deformed. 211a and the negative electrode 211b are rubbed against the outer package 251 .

For example, the difference between the distance La between a pair of sealing portions 262 and the width Wb of the negative electrode 211b is 1.6 times to 6.0 times, preferably 1.8 times to 5.0 times, more preferably 1.8 times to 5.0 times the thickness t of the positive electrode 211a and the negative electrode 211b. Preferably, it is 2.0 times or more and 4.0 times or less.

In other words, the distance Lb, the width Wb and the thickness t preferably satisfy the following formula 1.

[Formula 1]

Here, a is not less than 0.8 and not more than 3.0, preferably not less than 0.9 and not more than 2.5, more preferably not less than 1.0 and not more than 2.0.

In addition, FIG. 21C is a cross section including the lead wire 212a, corresponding to the cross section in the longitudinal direction of the secondary battery 250, the positive electrode 211a, and the negative electrode 211b. As shown in FIG. 21C , it is preferable to include a space 273 between the ends of the positive electrode 211 a and the negative electrode 211 b in the longitudinal direction and the outer package 251 in the folded portion 261 .

FIG. 21D shows a schematic cross-sectional view of the battery 250 when it is bent. FIG. 21D corresponds to a cross-section along line B1-B2 in FIG. 21A.

When the secondary battery 250 is bent, a part of the exterior body 251 located outside the bent portion is deformed to expand, and the other portion of the exterior body 251 located inside the bent portion is deformed to shrink. More specifically, the outer casing 251 deforms so that the amplitude of the wave is small and the period of the wave is large at the portion located outside the curve. On the other hand, the part of the exterior body 251 located inside the curve is deformed so that the amplitude of the wave is large and the period of the wave is small. By deforming the outer packaging body 251 as described above, the stress applied to the outer packaging body 251 due to bending can be alleviated, so that the material constituting the outer packaging body 251 itself does not necessarily need to be stretchable. As a result, the secondary battery 250 can be bent with a small force without damaging the exterior body 251 .

In addition, as shown in FIG. 21D , when the secondary battery 250 is bent, the positive electrode 211 a and the negative electrode 211 b are relatively displaced. At this time, since the ends of the plurality of stacked positive electrodes 211 a and negative electrodes 211 b on the sealing portion 263 side are fixed by the fixing member 217 , they are shifted so as to be closer to the folded portion 261 . Thus, the stress applied to the positive electrode 211a and the negative electrode 211b can be relaxed, and the positive electrode 211a and the negative electrode 211b themselves do not necessarily need to be stretchable. As a result, the secondary battery 250 can be bent without damaging the positive electrode 211a and the negative electrode 211b.

In addition, since the space 273 is included between the positive electrode 211a and the negative electrode 211b and the outer package 251, the positive electrode 211a and the negative electrode 211b located inside can be relatively shifted so as not to contact the outer package 251 during bending.

The secondary battery 250 illustrated in FIGS. 21A, 21B1 and 21B2, FIGS. 21C and 21D, and FIGS. 22A and 22B is not prone to breakage of the outer package and damage to the positive electrode 211a and the negative electrode 211b even if it is repeatedly bent and stretched. And battery characteristics are not easily deteriorated battery. By using the positive electrode active material described in the above embodiment for the positive electrode 211 a included in the secondary battery 250 , a battery with high capacity and excellent cycle characteristics can be realized.

Embodiment 4 In this embodiment, an example in which a secondary battery according to an embodiment of the present invention is mounted on an electronic device will be described.

First, FIG. 23A to FIG. 23G show an example in which the flexible secondary battery partially described in Embodiment 3 is mounted on an electronic device. Examples of electronic devices using flexible secondary batteries include televisions (also called televisions or television receivers), monitors for computers, digital cameras, digital video cameras, digital photo frames, mobile phones (also called For mobile phones, mobile phone devices), portable game machines, portable information terminals, audio reproduction devices, pachinko machines and other large game machines.

In addition, it is also possible to assemble a flexible secondary battery along a curved surface on the inner or outer walls of houses and high-rise buildings, or on the interior or exterior of automobiles.

Fig. 23A shows an example of a mobile phone. The mobile phone 7400 includes operation buttons 7403, an external connection port 7404, a speaker 7405, a microphone 7406, and the like in addition to a display unit 7402 incorporated in a housing 7401. In addition, the mobile phone 7400 has a secondary battery 7407 . By using the secondary battery according to one embodiment of the present invention as the above-mentioned secondary battery 7407, it is possible to provide a lightweight mobile phone with a long service life.

FIG. 23B shows a state in which mobile phone 7400 is bent. When the entire mobile phone 7400 is deformed by an external force and bent, the secondary battery 7407 installed inside is also bent. FIG. 23C shows the state of the secondary battery 7407 being bent at this time. The secondary battery 7407 is a thin storage battery. The secondary battery 7407 is fixed in a bent state. The secondary battery 7407 has a lead electrode 7408 electrically connected to a current collector. For example, the current collector is copper foil, and a part thereof is alloyed with gallium to improve the adhesion to the active material layer in contact with the current collector, thereby improving the reliability of the secondary battery 7407 in a bent state.

FIG. 23D shows an example of a bracelet-type display device. The portable display device 7100 includes a casing 7101 , a display unit 7102 , operation buttons 7103 , and a secondary battery 7104 . In addition, FIG. 23E shows a secondary battery 7104 that is bent. When the curved secondary battery 7104 is worn on the user's arm, the casing of the secondary battery 7104 is deformed so that the curvature of a part or all of the secondary battery 7104 changes. The value representing the degree of curvature at any point of the curve in the value of the equivalent circle radius is the radius of curvature, and the inverse of the radius of curvature is called curvature. Specifically, part or all of the casing or the main surface of the secondary battery 7104 is deformed within a range in which the radius of curvature is 40 mm or more and 150 mm or less. High reliability can be maintained as long as the radius of curvature in the main surface of the secondary battery 7104 is in the range of 40 mm to 150 mm. By using the secondary battery according to one embodiment of the present invention as the above-mentioned secondary battery 7104, a lightweight and long-lasting portable display device can be provided.

FIG. 23F is an example of a watch-type portable information terminal. The portable information terminal 7200 includes a housing 7201, a display unit 7202, a belt 7203, a buckle 7204, operation buttons 7205, input and output terminals 7206, and the like.

The portable information terminal 7200 can execute various applications such as mobile phone, e-mail, article reading and writing, music playback, network communication, and computer games.

The display surface of the display unit 7202 is curved, and display can be performed along the curved display surface. In addition, the display unit 7202 is equipped with a touch sensor, and can be operated by touching the screen with a finger, a stylus, or the like. For example, by touching the icon 7207 displayed on the display unit 7202, the application can be started.

The operation button 7205 may have various functions such as power switch, wireless communication switch, setting and canceling of silent mode, and setting and canceling of power saving mode, in addition to time setting. For example, by utilizing the operating system incorporated in the portable information terminal 7200, the functions of the operation buttons 7205 can be freely set.

In addition, the portable information terminal 7200 can implement short-range wireless communication standardized by communication. For example, hands-free calls can be made by communicating with a headset that can communicate wirelessly.

In addition, the portable information terminal 7200 has an input and output terminal 7206, which can directly send data to other information terminals or receive data from other information terminals through the connector. In addition, charging can also be performed through the input/output terminal 7206 . In addition, the charging operation can also be performed using wireless power supply instead of using the input/output terminal 7206 .

The display unit 7202 of the portable information terminal 7200 includes a secondary battery according to one embodiment of the present invention. By using the secondary battery according to one embodiment of the present invention, a lightweight and long-lasting portable information terminal can be provided. For example, the secondary battery 7104 shown in FIG. 23E in a bent state may be incorporated in the case 7201 , or the secondary battery 7104 may be incorporated in the belt 7203 in a bendable state.

The portable information terminal 7200 preferably includes sensors. As the sensors, for example, human body sensors such as fingerprint sensors, pulse sensors, and body temperature sensors, touch sensors, pressure sensors, and acceleration sensors are preferably installed.

FIG. 23G shows an example of an armband-type display device. The display device 7300 includes a display unit 7304 and a secondary battery according to one embodiment of the present invention. The display device 7300 may include a touch sensor in the display portion 7304 and be used as a portable information terminal.

The display surface of the display unit 7304 is curved, and display can be performed along the curved display surface. In addition, the display device 7300 can change the display situation by utilizing short-range wireless communication or the like which is standardized in communication.

The display device 7300 has input and output terminals, and can directly send data to other information terminals or receive data from other information terminals through the connector. In addition, charging can also be performed through the input and output terminals. In addition, the charging operation can also be performed using wireless power supply instead of using the input and output terminals.

By using the secondary battery according to one embodiment of the present invention as the secondary battery included in the display device 7300, it is possible to provide a lightweight and long-lasting display device.

23H , 24A to 24C , and 25 , an example in which the secondary battery excellent in cycle characteristics shown in the above embodiments is mounted on an electronic device will be described.

By using the secondary battery of one embodiment of the present invention as a secondary battery for daily electronic devices, it is possible to provide a product that is lightweight and has a long service life. For example, an electric toothbrush, an electric shaver, an electric beauty appliance, etc. are mentioned as an electronic device for daily use. Among these products, the secondary battery is expected to have a rod-like shape, small size, light weight, and large capacity so that users can easily hold it.

23H is a perspective view of a device known as an e-liquid containing smoking device (e-cigarette). In FIG. 23H , the electronic cigarette 7500 includes: an atomizer 7501 including a heating element; a secondary battery 7504 for powering the atomizer; and a cartridge 7502 including a liquid supply container and sensors. In order to improve safety, a protection circuit for preventing overcharge and overdischarge of the secondary battery 7504 may be electrically connected to the secondary battery 7504 . The secondary battery 7504 shown in FIG. 23H includes external terminals for connection with a charger. When being taken, the secondary battery 7504 is located at the top, so it is preferably shorter in overall length and lighter in weight. Since the secondary battery according to one embodiment of the present invention has a high capacity and excellent cycle characteristics, it is possible to provide a small and lightweight electronic cigarette 7500 that can be used for a long period of time.

Next, FIGS. 24A and 24B show an example of a tablet terminal that can be folded in half. The tablet terminal 9600 shown in FIG. 24A and FIG. 24B includes a housing 9630a, a housing 9630b, a movable part 9640 connecting the housing 9630a and the housing 9630b, a display part 9631, a display mode switching switch 9626, a switch 9627, a switching switch 9625, a fastener 9629, and Operate switch 9628. By using a flexible panel for the display portion 9631, a tablet terminal with a larger display portion can be realized. FIG. 24A shows a state where the tablet terminal 9600 is opened, and FIG. 24B shows a state where the tablet terminal 9600 is closed.

The tablet terminal 9600 includes a power storage body 9635 inside the casing 9630a and the casing 9630b. The electricity storage body 9635 is installed on the case 9630a and the case 9630b through the movable part 9640 .

In the display unit 9631, the whole or part thereof can be used as a touch panel area, and data can be input by touching images, characters, input boxes, etc. including icons displayed on the above area. For example, a keyboard is displayed on the entire surface of the display unit 9631 on the housing 9630a side, and information such as characters and images is displayed on the display unit 9631 on the housing 9630b side.

In addition, a keyboard is displayed on the display unit 9631 on the housing 9630b side, and information such as characters and images is displayed on the display unit 9631 on the housing 9630a side. In addition, keyboard buttons may be displayed on the display unit 9631 by making the display unit 9631 display a keyboard display switching button on the touch panel and touching it with a finger, a stylus, or the like.

In addition, the switches 9625 to 9627 may be used as an interface for switching various functions in addition to being used as an interface for operating the tablet terminal 9600 . For example, at least one of the switches 9625 to 9627 may be used as a switch for switching on/off the power of the tablet terminal 9600 . In addition, for example, at least one of the switches 9625 to 9627 may have: a function of switching display orientations such as portrait display and landscape display; and a function of switching black and white display or color display. In addition, for example, at least one of the switches 9625 to 9627 may have a function of adjusting brightness of the display part 9631 . In addition, the brightness of the display unit 9631 can be optimized according to the amount of external light detected by the light sensor incorporated in the tablet terminal 9600 during use. Note that, in addition to the light sensor, the tablet terminal may also have built-in other detection devices such as a gyroscope, an acceleration sensor, and other sensors for detecting inclination.

24B shows a state where the tablet terminal 9600 is folded in half, and the tablet terminal 9600 includes a case 9630 , a solar battery 9633 , and a charging and discharging control circuit 9634 including a DCDC converter 9636 . A secondary battery according to one embodiment of the present invention is used as the power storage body 9635 .

In addition, as described above, since the tablet terminal 9600 can be folded in half, the case 9630a and the case 9630b can be folded so as to overlap each other when not in use. By folding the case 9630a and the case 9630b, the display unit 9631 can be protected, and the durability of the tablet terminal 9600 can be improved. Furthermore, since the power storage body 9635 using the secondary battery according to one embodiment of the present invention has a high capacity and excellent cycle characteristics, it is possible to provide the tablet terminal 9600 that can be used for a long period of time.

In addition, the tablet terminal 9600 shown in FIG. 24A and FIG. 24B can also have the following functions: display various information (still images, dynamic images, text images, etc.); display the calendar, date or time, etc. on the display portion; Touch input for performing touch input operation or editing of information displayed on the display unit; control processing by various software (programs), etc.

By utilizing the solar cell 9633 mounted on the surface of the tablet terminal 9600, electric power can be supplied to a touch panel, a display section, an image signal processing section, and the like. Note that the solar battery 9633 can be provided on one surface or both surfaces of the casing 9630 to efficiently charge the storage body 9635 . By using a lithium-ion battery as the power storage body 9635, there is an advantage that miniaturization can be realized.

In addition, the configuration and operation of charge and discharge control circuit 9634 shown in FIG. 24B will be described with reference to the block diagram shown in FIG. 24C. Fig. 24C shows a solar battery 9633, a storage body 9635, a DCDC converter 9636, a converter 9637, a switch SW1 to a switch SW3, and a display unit 9631, and the storage body 9635, a DCDC converter 9636, a converter 9637, and switches SW1 to SW3 correspond to The charging and discharging control circuit 9634 shown in FIG. 24B.

First, an example of the operation when the solar cell 9633 generates electricity using external light will be described. The electric power generated by the solar cell is boosted or stepped down using a DCDC converter 9636 so that it becomes a voltage for charging the power storage body 9635 . Then, when the display unit 9631 is operated by the power from the solar cell 9633 , the switch SW1 is turned on, and the voltage is boosted or lowered by the converter 9637 to a voltage required by the display unit 9631 . In addition, when the display on the display unit 9631 is not being performed, the switch SW1 is turned off and the switch SW2 is turned on to charge the electricity storage body 9635 .

Note that the solar battery 9633 is shown as an example of a power generating unit, but it is not limited to this, and other power generating units such as piezoelectric elements (piezoelectric elements) and thermoelectric conversion elements (Peltier elements) may be used to store electricity. Body 9635 charging. For example, charging may be performed using a non-contact power transmission module capable of transmitting and receiving electric power in a wireless (non-contact) manner, or in combination with other charging methods.

FIG. 25 shows examples of other electronic devices. In FIG. 25 , a display device 8000 is an example of an electronic device using a secondary battery 8004 according to an embodiment of the present invention. Specifically, the display device 8000 corresponds to a display device for receiving television broadcasts, and includes a housing 8001, a display unit 8002, a speaker unit 8003, a secondary battery 8004, and the like. A secondary battery 8004 according to one embodiment of the present invention is provided inside the case 8001 . The display device 8000 can receive power from a commercial power source, and can use power stored in the secondary battery 8004 . Therefore, even when power supply from a commercial power source cannot be received due to a power outage or the like, the display device 8000 can be utilized by using the secondary battery 8004 according to one embodiment of the present invention as an uninterruptible power supply system.

As the display portion 8002, a semiconductor display device such as a liquid crystal display device, a light-emitting device including a light-emitting element such as an organic EL element in each pixel, an electrophoretic display device, a DMD (Digital Micromirror Device), a PDP (electronic Plasma Display Panel: Plasma Display Panel) and FED (Field Emission Display: Field Emission Display), etc.

In addition, the display device includes all display devices for displaying information, such as a display device for a personal computer or a display device for advertisement display, in addition to a display device for receiving television broadcasts.

In FIG. 25 , a mount type lighting device 8100 is an example of an electronic device using a secondary battery 8103 according to an embodiment of the present invention. Specifically, the lighting device 8100 includes a housing 8101, a light source 8102, a secondary battery 8103, and the like. Although FIG. 25 exemplifies the case where the secondary battery 8103 is installed inside the ceiling 8104 where the casing 8101 and the light source 8102 are installed, the secondary battery 8103 may be installed inside the casing 8101 . The lighting device 8100 can receive electric power supplied from a commercial power source, and can use electric power stored in a secondary battery 8103 . Therefore, even when power supply from a commercial power source cannot be received due to a power outage or the like, the lighting device 8100 can be utilized by using the secondary battery 8103 according to one embodiment of the present invention as an uninterruptible power supply system.

In addition, although a mount-type lighting device 8100 installed on a ceiling 8104 is illustrated in FIG. 25 , a secondary battery according to an embodiment of the present invention may be used on a side wall 8105, a floor 8106, or a window installed outside the ceiling 8104, for example. Mounted lighting equipment such as 8107 can also be used for desktop lighting equipment.

In addition, as the light source 8102, an artificial light source that artificially obtains light using electric power can be used. Specifically, examples of the aforementioned artificial light source include discharge lamps such as incandescent bulbs and fluorescent lamps, and light-emitting elements such as LEDs and organic EL elements.

In FIG. 25 , an air conditioner having an indoor unit 8200 and an outdoor unit 8204 is an example of an electronic device using a secondary battery 8203 according to one embodiment of the present invention. Specifically, the indoor unit 8200 includes a casing 8201, an air outlet 8202, a secondary battery 8203, and the like. Although the case where the secondary battery 8203 is provided in the indoor unit 8200 is illustrated in FIG. 25 , the secondary battery 8203 may be provided in the outdoor unit 8204 as well. Alternatively, a secondary battery 8203 may be provided in both the indoor unit 8200 and the outdoor unit 8204 . The air conditioner may be supplied with electric power from a commercial power source, or may use electric power stored in the secondary battery 8203 . In particular, when the secondary battery 8203 is provided in both the indoor unit 8200 and the outdoor unit 8204, even when power supply from a commercial power supply cannot be received due to a power outage or the like, by incorporating the The secondary battery 8203 is used as an uninterruptible power supply system, and an air conditioner can also be used.

In addition, although a split-type air conditioner composed of an indoor unit and an outdoor unit is illustrated in FIG. 25 , a secondary battery according to an embodiment of the present invention may also be used to have the functions of an indoor unit and an outdoor unit in one housing. functional integrated air conditioner.

In FIG. 25 , an electric refrigerator-freezer 8300 is an example of an electronic device using a secondary battery 8304 according to an embodiment of the present invention. Specifically, the electric refrigerator-freezer 8300 includes a casing 8301, a refrigerator door 8302, a freezer door 8303, a secondary battery 8304, and the like. In FIG. 25 , a secondary battery 8304 is provided inside a casing 8301 . The electric refrigerator-freezer 8300 may be supplied with electric power from a commercial power source, or may use electric power stored in a secondary battery 8304 . Therefore, the electric refrigerator-freezer 8300 can be utilized by using the secondary battery 8304 according to one embodiment of the present invention as an uninterruptible power supply system even when power supply from a commercial power source cannot be received due to a power outage or the like.

Among the electronic devices described above, high-frequency heating devices such as microwave ovens and electronic devices such as electric pans require high power in a short period of time. Therefore, by using the power storage device according to one embodiment of the present invention as an auxiliary power source for assisting power that cannot be sufficiently supplied by a commercial power source, it is possible to prevent a main switch of a commercial power source from tripping while using an electronic device.

In addition, in the time period when the electronic device is not used, especially in the time period when the ratio of the actually used power amount (referred to as the power usage rate) to the total amount of power that can be supplied by the supply source of the commercial power source is low, the power is stored. In the secondary battery, it is thereby possible to suppress an increase in the power usage rate in time periods other than the above-mentioned time periods. For example, in the case of electric refrigerator-freezer 8300, electric power is stored in secondary battery 8304 at night when the air temperature is low and refrigerator compartment door 8302 or freezer compartment door 8303 is not opened and closed. In addition, during the daytime when the temperature is high and the refrigerator compartment door 8302 or the freezer compartment door 8303 is opened and closed, the secondary battery 8304 is used as an auxiliary power source, thereby suppressing the power usage rate during the daytime.

By adopting one embodiment of the present invention, cycle characteristics and reliability of a secondary battery can be improved. In addition, by adopting one embodiment of the present invention, a high-capacity secondary battery can be realized, the characteristics of the secondary battery can be improved, and the secondary battery itself can be reduced in size and weight. Therefore, by mounting the secondary battery according to one embodiment of the present invention on the electronic device described in this embodiment, it is possible to provide an electronic device with a longer service life and a lighter weight. This embodiment mode can be implemented in combination with other embodiment modes as appropriate.

Embodiment 5 In this embodiment, an example in which a secondary battery according to an embodiment of the present invention is mounted on a vehicle is shown.

When a secondary battery is installed in a vehicle, next-generation clean energy vehicles such as hybrid electric vehicles (HEV), electric vehicles (EV) or plug-in hybrid electric vehicles (PHEV) can be realized.

In FIGS. 26A to 26C , a vehicle using a secondary battery according to an embodiment of the present invention is illustrated. A car 8400 shown in FIG. 26A is an electric car using an electric motor as a power source for running. Alternatively, the car 8400 is a hybrid car that can appropriately use an electric motor or an engine as a power source for running. By using the secondary battery of one embodiment of the present invention, a vehicle with a long running distance can be realized. In addition, the car 8400 is equipped with a secondary battery. As the secondary battery, the small secondary battery modules shown in FIGS. 11C and 11D can be used by being arranged on the floor of the vehicle. In addition, a battery pack obtained by combining a plurality of secondary batteries shown in FIGS. 16A to 16C may be installed on the floor portion of the vehicle. The secondary battery not only drives the electric motor 8406, but also supplies electric power to a light emitting device such as a headlight 8401 or a room lamp (not shown).

In addition, the secondary battery can supply electric power to display devices such as a speedometer and a tachometer included in the automobile 8400 . In addition, the secondary battery can supply electric power to semiconductor devices such as a navigation system included in the automobile 8400 .

In the car 8500 shown in FIG. 26B , the secondary battery included in the car 8500 can be charged by receiving electric power from an external charging device using a plug-in method or a non-contact power supply method. FIG. 26B shows a case where secondary batteries 8024 and 8025 installed in a car 8500 are charged from a ground-mounted charging device 8021 via a cable 8022 . When charging is performed, the charging method, the specification of the connector, and the like can be appropriately performed in accordance with a prescribed method such as CHAdeMO (registered trademark) or a combined charging system "Combined Charging System". As the charging device 8021, a charging station installed in a commercial facility or a power supply at home may be used. For example, secondary batteries 8024, 8025 mounted in the car 8500 can be charged by externally supplying electric power using plug-in technology. Charging can be performed by converting AC power into DC power with a conversion device such as an AC/DC converter.

In addition, although not shown in the figure, the power receiving device may be mounted on the vehicle, and electric power may be supplied contactlessly from the power transmitting device on the ground for charging. When a non-contact power supply method is used, charging can be performed not only while parking but also while driving by assembling a power transmission device on a road or an outer wall. In addition, it is also possible to transmit and receive electric power between vehicles using this non-contact power feeding method. Furthermore, a solar battery may be installed outside the vehicle, and the secondary battery may be charged while the vehicle is parked or driven. Such non-contact power supply can be realized using an electromagnetic induction method or a magnetic field resonance method.

FIG. 26C is an example of a two-wheeled vehicle using a secondary battery according to an embodiment of the present invention. A scooter 8600 shown in FIG. 26C includes a secondary battery 8602 , a rearview mirror 8601 and a turn signal 8603 . The secondary battery 8602 can supply power to the direction light 8603 .

In addition, in the scooter 8600 shown in FIG. 26C , the secondary battery 8602 can be stored in the under-seat storage box 8604 . Even if the under-seat storage box 8604 is small, the secondary battery 8602 can be stored in the under-seat storage box 8604 . The secondary battery 8602 is detachable, so when charging, the secondary battery 8602 may be carried indoors, charged, and stored before driving.

By adopting one embodiment of the present invention, the cycle characteristics and capacity of the secondary battery can be improved. Accordingly, the size and weight of the secondary battery itself can be reduced. In addition, if the secondary battery itself can be reduced in size and weight, it will contribute to the reduction in weight of the vehicle, thereby extending the driving distance. In addition, a secondary battery installed in a vehicle may be used as an electric power supply source outside the vehicle. In this case, it is possible to avoid, for example, the use of commercial power sources at times of peak power demand. Avoiding the use of commercial power during times of peak electricity demand contributes to energy savings and a reduction in CO2 emissions. In addition, if the cycle characteristics are excellent, the secondary battery can be used for a long period of time, thereby reducing the usage of rare metals such as cobalt.

This embodiment mode can be implemented in combination with other embodiment modes as appropriate. Example 1

In this example, the results of producing a positive electrode active material 100 according to one embodiment of the present invention and lithium cobaltate as a comparative example and analyzing them using XRD will be described.

[Manufacture of positive electrode active material] "Sample 01" The sample 01 of the positive electrode active material according to one embodiment of the present invention is formed by the following method: adding magnesium and fluorine to the starting material to produce particles of lithium cobaltate, and then subjecting it to heating.

In sample 01, as described in step S11 of Embodiment 1, lithium carbonate as a lithium source as a starting material, cobalt oxide as a cobalt source, magnesium oxide as a magnesium source, and lithium fluoride as a fluorine source are prepared. . Weighing was performed so that the ratio of each element became Li _1.02 Co _0.99 Mg _0.01 O _1.98 F _0.02 .

Next, as step S12, starting materials are mixed. The mixing was performed at 250 rpm for 2 hours using a ball mill with zirconia balls.

Next, as step S13, the mixed material is placed in a furnace made of alumina (hereinafter referred to as an alumina furnace) and heated. The heating was carried out under the following conditions: using a muffle furnace; the flow rate of the dry air atmosphere was 10 L/min; the temperature was maintained at 950° C. (the temperature increase was 200° C./hour); the temperature was maintained for 10 hours. The cooling time from the holding temperature to room temperature is set to 10 hours or more and 15 hours or less.

Since the coating treatment of titanium and aluminum is not performed, step S14 is not performed.

Next, as step S15, the lithium cobaltate particles containing magnesium and fluorine synthesized in step S13 are placed in an alumina melting furnace and heated. The heating was performed under the following conditions: a muffle furnace was used; the flow rate of the oxygen atmosphere was 10 L/min; the temperature was kept at 900° C. (the temperature increase was 200° C./hour); the temperature was kept at 2 hours. The cooling time from the holding temperature to room temperature is set to 10 hours or more and 15 hours or less.

Then, pulverization is performed. The pulverization process was performed by sieving, and a sieve with a hole diameter of 53 mm was used.

Finally, the particles were collected to obtain the positive electrode active material of sample 01. It is known that the concentration of magnesium and fluorine in the surface layer of the positive electrode active material produced under the above conditions is higher than that in the inside.

"Sample 02" The sample 02 of the positive electrode active material according to one embodiment of the present invention is formed by heating lithium cobaltate particles containing magnesium and fluorine.

In sample 02, lithium cobaltate particles (manufactured by Nippon Chemical Industry Co., Ltd., trade name: C-20F) were used as a starting material. Accordingly, step S12 and step S13 described in the first embodiment are omitted in the sample 02. The above lithium cobaltate particles have a particle diameter (D50) of about 20 mm and contain fluorine, magnesium, calcium, sodium, silicon, sulfur, and phosphorus in a region that can be analyzed by XPS. In addition, step S14 is not performed because the coating treatment of titanium and aluminum is not performed.

Next, as step S15, the lithium cobalt oxide particles are placed in an alumina melting furnace and heated. The heating was carried out under the following conditions: using a muffle furnace; the flow rate of the dry air atmosphere was 5 L/min; the temperature was maintained at 800° C. (the temperature increase was 200° C./hour); the temperature was maintained for 2 hours. The cooling time from the holding temperature to room temperature is set to 10 hours or more and 15 hours or less. Then, it was screened and collected in the same manner as sample 01. It is known that the concentrations of magnesium and fluorine in the surface layer of the positive electrode active material produced under the above conditions are also higher than those in the inside.

"Sample 03" In sample 03, which is a positive electrode active material according to an embodiment of the present invention, a positive electrode active material of lithium cobaltate containing magnesium and fluorine covered with titanium was formed by a sol-gel method.

Lithium cobaltate particles (manufactured by Nippon Chemical Industry Co., Ltd., trade name: C-20F) were also used as the starting material of sample 03. Thus, step S12 and step S13 are omitted.

Next, as step S14, the lithium cobaltate particles are covered with a material containing titanium. Specifically, an isopropanol solution of TTIP was produced by dissolving TTIP in isopropanol. Lithium cobaltate particles were mixed in this solution. It mixed so that the ratio of TTIP and lithium cobaltate containing magnesium and fluorine might become 0.004 ml/g.

The liquid mixture was stirred at 25°C under a humidity of 90%RH with a magnetic stirrer uncovered for 72 hours. Through the above treatment, water in the atmosphere and TTIP undergo hydrolysis and polycondensation reactions, thereby forming a layer containing titanium on the surface of the lithium cobalt oxide particles containing magnesium and fluorine.

Centrifuge the mixed solution after the above treatment, and collect the precipitate. Centrifugation was performed at 3000 rpm for 1 minute, and isopropanol was used for washing.

The collected precipitate was dried at 70° C. for 3 hours in a circulating drying oven.

Next, as step S15 , the lithium cobaltate particles covered with the titanium-containing material are placed in an alumina melting furnace and heated. The heating was performed under the following conditions: using a muffle furnace; the flow rate of the oxygen atmosphere was 10 L/min; the temperature was kept at 800° C. (the temperature increase was 200° C./hour); the temperature was kept at 2 hours. The cooling time from the holding temperature to room temperature is set to 10 hours or more and 15 hours or less. Then, it was screened and collected in the same manner as sample 01. It is known that the concentrations of titanium, magnesium, and fluorine in the surface layer of the positive electrode active material produced under the above conditions are higher than those in the inside. In addition, it is also known that the peak of the titanium concentration is located in a deeper region than the peak of the magnesium concentration.

"Sample 04" In sample 04, which is a positive electrode active material according to an embodiment of the present invention, a positive electrode active material including lithium cobaltate particles containing magnesium and fluorine covered with aluminum was formed by a sol-gel method.

Lithium cobaltate particles (manufactured by Nippon Chemical Industry Co., Ltd., trade name: C-20F) were also used as the starting material of sample 04. Thus, step S12 and step S13 are omitted.

Next, as step S14, the lithium cobaltate particles are covered with a material containing aluminum. Specifically, aluminum isopropoxide is dissolved in isopropanol to produce an isopropanol solution of aluminum isopropoxide. Lithium cobaltate particles were mixed with this solution. The aluminum isopropoxide was mixed so that the ratio of the lithium cobaltate containing magnesium and fluorine was 0.0279 g/g.

The liquid mixture was stirred at 25°C under a humidity of 90%RH with a magnetic stirrer uncovered for 8 hours. Through the above treatment, water in the atmosphere and aluminum isopropoxide undergo hydrolysis and polycondensation reactions, thereby forming a layer containing aluminum on the surface of the lithium cobaltate particles containing magnesium and fluorine.

Filter the treated mixture and collect the residue. Kiriyama filter paper (No. 4) was used as a filter for filtration, and isopropanol was used for washing.

The collected residue was dried at 70° C. for 1 hour in a vacuum bell jar.

Next, as step S15, the lithium cobaltate particles covered with the material containing aluminum are placed in an alumina melting furnace and heated. The heating was performed under the following conditions: using a muffle furnace; the flow rate of the oxygen atmosphere was 10 L/min; the temperature was kept at 800° C. (the temperature increase was 200° C./hour); the temperature was kept at 2 hours. The cooling time from the holding temperature to room temperature is set to 10 hours or more and 15 hours or less. Then, it was screened and collected in the same manner as sample 01. It is known that the concentrations of aluminum, magnesium, and fluorine in the surface layer of the positive electrode active material produced under the above conditions are higher than those in the inside. In addition, it is also known that the peak of the aluminum concentration is located in a region deeper than the peak of the magnesium concentration.

"Sample 05" In Sample 05 as a comparative example, lithium cobaltate containing magnesium and fluorine (manufactured by Nippon Chemical Industry Co., Ltd., trade name: C-20F) was directly used without sol-gel treatment or heat treatment.

"Sample 06" In Sample 06 as a comparative example, lithium cobaltate particles not containing magnesium and fluorine were covered with aluminum by the sol-gel method.

In sample 06, lithium cobaltate particles (manufactured by Nippon Chemical Industry Co., Ltd., trade name: C-5H) were used as a starting material. Thus, step S12 and step S13 are omitted. Note that the above-mentioned lithium cobaltate particles have a particle diameter (D50) of about 5 mm and are lithium cobaltate particles in which magnesium cannot be detected by XPS or the like.

Next, as step S14, the lithium cobaltate particles are covered with a material containing aluminum. Specifically, aluminum isopropoxide is dissolved in isopropanol to produce an isopropanol solution of aluminum isopropoxide. Lithium cobaltate particles were mixed with this solution. Mixing was performed so that the ratio of aluminum isopropoxide to lithium cobaltate containing magnesium and fluorine was 0.0917 g/g.

Stirring, collection, and drying were performed in the same manner as sample 04.

Next, as step S15, the lithium cobaltate particles covered with the material containing aluminum are heated, cooled, and collected. Except that the heating temperature was set to 500° C., it was manufactured under the same conditions as Sample 04.

Table 1 shows the manufacturing conditions of Sample 01 to Sample 06.

[Manufacture of Secondary Battery] A coin-type secondary battery of CR2032 (diameter: 20 mm, height: 3.2 mm) was manufactured using the positive electrode active material of Sample 01 to Sample 06 manufactured above.

As the positive electrode, a positive electrode produced by mixing the above-produced positive electrode active material (LCO): acetylene black (AB): polyvinylidene fluoride (PVDF) in a weight ratio of 95:3:2 was used. The slurry is coated on the current collector.

Lithium metal was used as a counter electrode.

As an electrolyte contained in the electrolytic solution, 1 mol/L lithium hexafluorophosphate (LiPF ₆ ) was used. As the electrolytic solution, an electrolytic solution obtained by mixing ethylene carbonate (EC), diethyl carbonate (DEC) and 2 wt % vinylene carbonate (VC) at a volume ratio of 3:7 was used.

A 25 mm thick polypropylene was used as the separator.

The positive electrode can and the negative electrode can are formed of stainless steel (SUS).

[XRD after initial charging] The secondary batteries using the positive electrode active materials of Sample 01 to Sample 06 were subjected to CCCV charging at a predetermined voltage. Specifically, after the constant current charging was performed at 0.5C until the predetermined voltage was reached, the constant voltage charging was performed until the current value became 0.01C. Next, the charged secondary battery was disassembled in a glove box in an argon atmosphere, and the positive electrode was taken out, and washed with DMC (dimethyl carbonate) to remove the electrolytic solution. Next, analysis was performed by CuKa1 line powder XRD analysis. In addition, in this analysis, a fully automatic multi-purpose X-ray diffraction device D8 ADVANCE manufactured by Bruker AXS was used. Although the XRD apparatus is set to the powder sample mode, the height of the sample is set to the measurement surface required by the apparatus. In addition, the sample was set flat without bending it.

FIG. 27 shows an XRD pattern of the positive electrode after charging the secondary battery using the positive electrode active material of Sample 01 at 4.6V. For comparison, the patterns of the pseudo-spinel crystal structure and the H1-3 crystal structure similar to those in FIG. 3 are also shown. In addition, it can be seen that the pseudo-spinel type crystal structure and the H1-3 type crystal structure are mixed in the sample 01 when charged at 4.6V. In addition, it is estimated to have a pseudo-spinel crystal structure of 66 wt% by Rietveld analysis.

FIG. 28 shows XRD patterns of positive electrodes after charging the secondary battery using the positive electrode active material of Sample 02 at 4.1V, 4.2V, 4.3V, 4.4V, 4.5V, 4.6V, 4.7V, and 4.8V. It can be seen that sample 02 when charged at 4.6V has a pseudo-spinel crystal structure. In addition, it is presumed that the sample 02 charged at 4.7 V or more has a structure different from the pseudo-spinel crystal structure, and the width of the peak is widened, and the crystallinity is lowered.

FIG. 29 shows XRD patterns of positive electrodes after charging the secondary battery using the positive electrode active material of Sample 03 at 4.1V, 4.2V, 4.3V, 4.4V, 4.5V, 4.6V, 4.7V, and 4.8V. It can be seen that sample 03 when charged at 4.6V has a pseudo-spinel crystal structure. In addition, sample 03 charged at 4.6V showed a more distinct pattern, and it is presumed that the crystal structure other than the pseudo-spinel type was less than sample 02 charged at 4.6V. In addition, it is estimated that sample 03 when charged at 4.7 V or higher has a crystal structure different from that of pseudo-spinel, and that the width of the peak is widened, and the crystallinity is lowered.

FIG. 30 shows XRD patterns of positive electrodes after charging the secondary battery using the positive electrode active material of Sample 04 at 4.6V, 4.7V, and 4.8V. It can be seen that sample 04 when charged at 4.6V and 4.7V has a pseudo-spinel crystal structure. In addition, it is estimated that sample 04 charged at 4.8 V has a crystal structure different from that of pseudo-spinel, and that the width of the peak is widened and the crystallinity is lowered.

31 shows XRD patterns of positive electrodes charged at 4.1V, 4.2V, 4.3V, 4.4V, 4.5V, 4.6V, 4.7V, and 4.8V for a secondary battery using the positive electrode active material of sample 05 of the comparative example . It can be seen that sample 05 of the comparative example has an H1-3 type crystal structure and does not have a pseudo-spinel type crystal structure when charged at 4.6 V or more and 4.7 V or less (the peak from 43.5° to 46° (2q) is particularly characteristic ). In addition, it was found that the H1-3 crystal structure was changed between 4.5V and 4.6V. In addition, it is estimated that sample 05 when charged at 4.8 V has a crystal structure different from the pseudo-spinel crystal structure and the H1-3 crystal structure, and the width of the peak is broadened, and the crystallinity is lowered.

FIG. 32 shows an XRD pattern of the positive electrode after charging the secondary battery using the positive electrode active material of sample 06 of the comparative example at 4.6V. It can be seen that sample 06 when charged at 4.6V has an H1-3 type crystal structure.

[XRD after Multiple Charges] Next, samples 02, 03, and sample 05 of the comparative example were charged multiple times at 4.6V and analyzed by XRD. Specifically, a sample that was charged with CCCV at 4.6V was taken as a sample that was charged once. In addition, after performing CCCV charging at 4.6V, a constant current discharge (CC discharge) was performed until the discharge voltage became 2.5V, and then a sample was subjected to CCCV charging at 4.6V as a sample charged twice. Likewise, some samples were charged nine times.

FIG. 33 shows XRD patterns of the positive electrode after charging the secondary battery using the positive electrode active material of Sample 02 once at 4.6 V and after charging it twice. It is presumed that the crystallinity is low since the H1-3 type crystal structure and other structures are present in addition to the pseudo-spinel type crystal structure at the time of the first charge. However, in the second charge, since structures other than the pseudo-spinel crystal structure decreased, the crystallinity was improved compared with the first charge.

FIG. 34 shows XRD patterns of positive electrodes after charging the secondary battery using the positive electrode active material of Sample 03 at 4.6 V once, twice, and nine times. It is presumed that sample 03 also has low crystallinity at the time of the first charge because there are H1-3 type crystal structure and other structures in addition to the pseudo-spinel type crystal structure. However, at the time of charging after the second time, since structures other than the pseudo-spinel crystal structure decrease, the pseudo-spinel crystal structure maintains high crystallinity.

FIG. 35 shows XRD patterns of the positive electrode after charging the secondary battery using the positive electrode active material of sample 05 of the comparative example at 4.6 V once and twice. Sample 05 had the H1-3 type crystal structure at both the first charge and the second charge. The characteristic is also evident when paying attention to the peak existing in the range of 43.5° to 46° (2q).

[XRD after Multiple Discharges] Next, sample 02, sample 03, and sample 05 of the comparative example were charged ten times and analyzed by XRD. Specifically, charge and discharge after CCCV charge (4.6V) and then CC discharge (2.5V) was repeated ten times, and then the discharged secondary battery was disassembled to take out the positive electrode and analyzed by XRD.

FIG. 36 shows XRD patterns of the positive electrodes after sample 02, sample 03, and sample 05 of the comparative example were discharged ten times. For comparison, the same patterns of LiCoO ₂ (O3), pseudo-spinel crystal structure, and H1-3 crystal structure as in FIG. 3 are also shown. Sample 02, Sample 03, and Sample 05 all have the structure of LiCoO ₂ (O3). However, in sample 05, the width of the diffraction peak from a plane perpendicular to the c-axis, such as the (003) plane and the (006) plane in LiCoO ₂ (03), is widened and the crystallinity is lowered. On the other hand, it is presumed that sample 02 and sample 03 maintained high crystallinity because no deviation of the CoO ₂ layer occurred, and there was little deterioration after charging ten times.

[Volume Change] Next, the lattice constant and the crystal structure were estimated from the XRD pattern of each charge depth of the sample 03. Then, the volume per unit cell of each crystal structure was obtained and compared with the volume before charging. In addition, in order to facilitate comparison with other crystal structures, the c-axis of the H1-3 type crystal structure was calculated using a half value of the unit cell.

Table 2 shows the lattice constant and crystal structure estimated from the XRD pattern of each charge depth of sample 03.

It is estimated that when charged at 4.1 V or more and 4.5 or less, all have a two-phase crystal structure belonging to the space group R-3m. This may be due to a difference in the depth of charge generated inside or between particles of each positive electrode active material. In Table 2, they are represented by R-3m(1) and R-3m(2).

When charging at 4.6V, it is presumed that the pseudo-spinel type crystal structure and the H1-3 type crystal structure are mixed. In addition, according to Rietwald analysis, it is speculated that the pseudo-spinel crystal structure accounts for more than 77wt%.

In addition, when charging at 4.7V, it is presumed that the H1-3 type crystal structure and the O1 type crystal structure are mixed.

In addition, the volume change rate of the pseudo-spinel crystal structure from the O3 crystal structure is 2.5% or less, more specifically 2.2% or less, while the volume change rate of the H1-3 crystal structure from the O3 crystal structure is 2.5% or less. rate is above 3.5%.

FIG. 37 shows the case where the volume change rates shown in Table 2 are expressed as a graph. Only the markings representing O3: Depth of Charge 0 refer to the upper horizontal axis of the graph. In addition, in FIG. 37 , each mark shows that the crystal structure is presumed to be any one of the following structures: R-3m(1)(2); pseudo-spinel type crystal structure; H1-3 type crystal structure; and O1 type crystal structure.

As can be seen from Table 2 and FIG. 37 , the volume change per unit cell of the pseudo-spinel crystal structure is smaller than that of the H1-3 crystal structure. In addition, it can be seen that sample 03 charged at 4.6V has a pseudo-spinel crystal structure of 77 wt% or more, and its crystal structure and volume change are suppressed.

[Cycle Characteristics] Next, the cycle characteristics of the secondary batteries using Sample 01, Sample 03, and Sample 05 were evaluated.

Note that the sample 01 and sample 03 whose cycle characteristics were evaluated are different from the batches of the XRD analysis samples, and the manufacturing conditions are slightly different, so the asterisks are attached in the graph, but there is no great difference as a characteristic of the positive electrode active material. Specifically, the sample 01 was subjected to the first heat treatment at 1000°C. Sample 03 used 0.01 ml/g of TTIP for sol-gel treatment and underwent a second heat treatment under dry air atmosphere.

The coin cell is composed of positive active material (LCO), acetylene black (AB), and polyvinylidene fluoride (PVDF) mixed in a ratio of LCO:AB:PVDF=95:2.5:2.5 (weight ratio), and other manufacturing conditions are the same.

The cycle test is carried out at 25°C, the charge is CCCV (0.5C, 4.6V, the termination current is 0.01C), and the discharge is CC (0.5C, 2.5V). Here, 1C is set to 137 mA/g, which is the current value per unit mass of the positive electrode active material.

FIG. 38A shows the discharge capacities of Sample 01, Sample 03, and Sample 05, and FIG. 38B shows the retention rate of the discharge capacity. The retention rate of the discharge capacity at 40 cycles of the sample 05 of the comparative example dropped to 40.9%. On the other hand, the initial capacity of the positive electrode active material according to one embodiment of the present invention is about the same as that of the comparative example, and both sample 01 and sample 03 exhibit excellent cycle characteristics, and sample 03 is 78.4% at 100 cycles, Sample 01 was 67.5% at 70 cycles.

It can be seen that the positive electrode active material according to one embodiment of the present invention exhibits good cycle characteristics even when charged and discharged at a high voltage such as 4.6V.

Thus, it can be seen that in samples 01 to 04 of the positive electrode active material according to one embodiment of the present invention, 60% or more of the pseudo-spinel crystal structure was obtained by charging at 4.6V. The difference in crystal structure and volume between the pseudo-spinel crystal structure and the discharged state is smaller than that of the H1-3 crystal structure, so repeated charge and discharge are less likely to deteriorate. Therefore, when charging at a high voltage, as long as it is a positive electrode active material having a pseudo-spinel crystal structure, even if it is charged and discharged at a high voltage, its cycle characteristics are excellent.

On the other hand, it can be seen that when the samples 05 and 06 of the comparative example were charged at 4.6V, the pseudo-spinel crystal structure did not appear or was very little, and the H1-3 crystal structure was mainly present. Since the H1-3 type crystal structure and the O3 type crystal structure have a large difference in crystal structure and volume, they tend to deteriorate. Therefore, Sample 05 and Sample 06 are materials that cannot withstand high-voltage charging, and the discharge capacity is actually remarkably lowered.

In addition, the sample 05 of the comparative example contains magnesium and fluorine similarly to the sample 01, but has mainly the H1-3 type crystal structure when charged at 4.6V, so the cycle characteristics deteriorate. Thus, it can be seen that one embodiment of the present invention is characterized in that the positive electrode active material has little change in crystal structure accompanying charge and discharge, and that the above characteristics cannot be judged only by the elements contained therein. Example 2

In this example, the results of producing the positive electrode active material 100 according to one embodiment of the present invention and lithium cobaltate as a comparative example and analyzing them using ESR will be described.

[Manufacture of positive electrode active material] "Sample 11A and Sample 11B" The positive electrode active material formed by adding magnesium and fluorine to the starting material and performing the first heat treatment was used as sample 11A, and the positive electrode that was further subjected to the second heat treatment The active material was taken as sample 11B.

Lithium carbonate, cobalt oxide, magnesium oxide, and lithium fluoride are weighed so that the ratio of each element becomes Li _1.02 Co _0.99 Mg _0.01 O _1.98 F _0.02 as steps S11 and S12, and then mixed. The first heating in step S13 was carried out under the following conditions: using an alumina furnace; the flow rate of the dry air atmosphere was 10 L/min; the temperature was kept at 1000° C. (the temperature was raised to 200° C./hour); the temperature was kept at 10 hours. The cooling time from the holding temperature to room temperature is set to 10 hours or more and 15 hours or less. The particles of lithium cobaltate containing magnesium and fluorine synthesized by the first heat treatment were taken as sample 11A.

Next, the lithium cobaltate particles containing magnesium and fluorine of the sample 11A were put into an alumina melting furnace, and the second heat treatment in step S15 was performed. The heating was carried out under the following conditions: the flow rate of the dry air atmosphere was 10 L/min; the holding temperature was 800° C. (the temperature increase was 200° C./hour); and the holding temperature was 2 hours. The cooling time from the holding temperature to room temperature is set to 10 hours or more and 15 hours or less. The particles produced through the above-mentioned steps were taken as sample 11B.

«Sample 12B» A positive electrode active material produced by performing the first and second heat treatments without adding magnesium and fluorine was used as a sample 12B of a comparative example.

It manufactured similarly to sample 11B except having weighed lithium carbonate and cobalt _oxide so that the ratio _of each element might become _Li1Co1O2 .

[ESR] FIG. 39 and FIGS. 40A to 40C show the results of analyzing the sample 11A, the sample 11B, and the sample 12B by ESR. Figure 39 is the signal measured at room temperature. 40A to 40C are graphs showing enlarged results of low temperature (10K) measurements for comparison with a sharp signal around 320 mT.

As shown in FIG. 39 , in sample 12B and sample 11A, a signal with a wide width around 120 mT to 150 mT was detected, but in sample 11B, the signal was below the detection lower limit. This signal corresponds to oxygen tetracoordinated Co (position A in FIG. 5A and FIG. 5B ).

From this, it can be seen that the sample 12B not containing magnesium and fluorine and the sample 11A containing magnesium and fluorine but not subjected to the second heat treatment have Co ₃ O ₄ with a spinel crystal structure; Co ₃ O ₄ having a spinel crystal structure in the processed sample 11B was below the lower limit of detection.

In addition, as shown in FIGS. 40A to 40C , a sharp peak centered around 320 mT was detected in all the samples. The above signal corresponds to oxygen hexa-coordinated Co (position B in FIG. 5A and FIG. 5B ).

Among them, a shoulder peak was observed around 312 mT in sample 11A of FIG. 40B and sample 11B of FIG. 40C , but was not observed in sample 12B of FIG. 40A . The above peaks show the presence of Mg near Co. Thus, it can be seen that the positive electrode active material can also be judged to contain Mg by ESR. Example 3

In the present example, it was confirmed by calculation which element is likely to have a pseudo-spinel crystal structure when it is charged at a high voltage when it is dissolved in a solid solution.

As shown in FIG. 2 , the H1-3 type crystal structure is a structure in which CoO ₂ structures such as P-3m1(O1) and LiCoO ₂ structures such as R-3m(O3) are alternately laminated.

From this, it can be considered that by increasing the structure belonging to P-3m1 to about half, it is easy to have the H1-3 type crystal structure; on the contrary, by making the structure belonging to R-3m account for more than 50%, it is easy to have Pseudo-spinel crystal structure of R-3m. Then, using the crystal structure models of P-3m1 and R-3m to reproduce the positive electrode active material in the high-voltage charge state, the stability energy when Mg, Al, and Ti were contained was calculated.

As a crystal structure model in a high-voltage charged state, a structure in which all Li was removed from R-3m(O3) described in FIG. 2 and P-3m1(O1) were used. Next, the case where Mg, Al, or Ti is inserted into the most stable position between the CoO ₂ layers and the case where the Co site is substituted by Mg, Al, or Ti are respectively calculated as described below.

FIG. 41A1 shows a crystal structure model of P-3m1 when Mg, Al, or Ti is located between CoO2 layers, and FIG. _41A2 shows a crystal structure model of R-3m when Mg, Al, or Ti is located between _CoO2 layers. FIG. 41B1 shows a crystal structure model of P-3m1 when Mg, Al, or Ti is at the Co site, and FIG. 41B2 shows a crystal structure model of R-3m when Mg, Al, or Ti is at the Co site. In addition, Table 3 shows calculation conditions.

In the case of intercalating Mg between _CoO2 layers, the energy difference DE (eV) between the space group P-3m1 structure and the space group R-3m structure was obtained by the following formula. As the elemental energy for intercalation and substitution, atomic energy is used.

：空間群R-3m的結晶結構且將一個Mg原子嵌入CoO₂ 層間的模型(相當於圖41A2的結構b)的能量

：空間群P-3m1的結晶結構且將一個Mg原子嵌入CoO₂ 層間的模型(相當於圖41A1的結構a)的能量[Formula 2]

: The energy of the model of the crystal structure of space group R-3m and one Mg atom intercalated between CoO ₂ layers (equivalent to structure b in Fig. 41A2)

: The energy of the model of the crystal structure of space group P-3m1 and one Mg atom intercalated between CoO ₂ layers (equivalent to structure a in Fig. 41A1)

Similarly, when the Co site is substituted by Mg, the difference in energy is obtained by the following formula.

：空間群R-3m的結晶結構且Co被一個Mg原子取代的模型(相當於圖41B2的結構d)的能量

：空間群P-3m1的結晶結構且Co被一個Mg原子取代的模型(相當於圖41B1的結構c)的能量[Formula 3]

: The energy of the model (equivalent to structure d in Fig. 41B2) of the crystal structure of space group R-3m with Co replaced by one Mg atom

: The energy of the model (equivalent to structure c in Fig. 41B1) of the crystal structure of space group P-3m1 with Co replaced by one Mg atom

42A and 42B show the calculation results of other elements performed in the same manner as above. For comparison, the results when there is no intercalation or substitution and when Li is intercalated between _CoO2 layers are also shown.

FIG. 42A is a graph showing the stabilization energy DE when Al, Ti, Mg, or Li is intercalated between CoO ₂ layers. The DE of each element is negative, which means that the structure of space group R-3m is more stable than that of P-3m1. In addition, the value of each element is lower than Li. In other words, the positive electrode active material containing the above-mentioned elements between CoO ₂ layers is more likely to have an R-3m structure than pure LiCoO ₂ even in a high-voltage charging state. It can be seen that Mg is the most effective among Al, Ti, and Mg.

Fig. 42B is a graph of the stabilization energy DE when the Co site is substituted by Al, Ti, Mg. The DE values of all elements became positive, showing that the structure of P-3m1 was more stable. The values of Al and Ti are lower than the case of non-substitution (the case where Co is present), but the value of Mg is higher than the case of non-substitution.

From this, it can be seen that Mg present between CoO ₂ layers has a high effect of maintaining R-3m, whereas Mg present at the Co site has no such effect.

Next, when calculating the R-3m(O3) crystal structure in a discharged state in which all lithium ions are intercalated, which one of Al, Ti, or Mg is substituted for the Li site or the Co site is more stable. The calculation method is the same as in Fig. 42A and Fig. 42B. Fig. 43 shows the results.

When any of the Li site and the Co site is substituted, the DE of Al and Ti become approximately the same negative value. In addition, the DE of Ti is smaller. From this, it can be seen that Al and Ti tend to be easily solid-dissolved in LiCoO ₂ , among which Ti is more likely to be solid-dissolved.

On the other hand, regarding the comparison of Mg between the Li site and the Co site, the Li site is larger and stable. From this, it can be seen that Mg is more likely to enter the Li site than the Co site. In addition, since DE is a positive value at each substitution, it can be said that Mg tends to be less likely to dissolve in LiCoO ₂ . The above-mentioned tendency can explain the phenomenon that a part of Mg segregates in the surface layer part, the vicinity of the crystal grain boundary, and the like.

From the above description, it is shown that when Mg exists between the CoO ₂ layers (Li sites), the R-3m structure is easily maintained even in the high-voltage charging state where many Li are extracted, and the pseudo-spinel type is easily formed. crystalline structure. From this, it can be considered that it is important that Mg, which tends to enter the Li site of LiCoO ₂ , is surely located at the Li site and not located at the Co site in the manufacturing process including the second heat treatment.

100‧‧‧positive active material 200‧‧‧active material layer 201‧‧‧graphene compound 211a‧‧‧positive electrode 211b‧‧‧negative electrode 212a‧‧‧conducting wire 212b‧‧‧conducting wire 214‧‧‧separator 215a‧‧ ‧Joint part 215b ‧Edge line 272‧‧‧Valley line 273‧‧‧Space 300‧‧‧Secondary battery 301‧‧‧Positive electrode can 302‧‧‧Negative electrode can 303‧‧‧Gasket 304‧‧‧Positive electrode 305‧‧‧Positive electrode assembly Appliance 306‧‧‧positive active material layer 307‧‧‧negative electrode 308‧‧‧negative electrode current collector 309‧‧‧negative electrode active material layer 310‧‧‧separator 500‧‧‧secondary battery 501‧‧‧positive electrode current collector 502 ‧‧‧positive active material layer 503‧‧‧positive electrode 504‧‧‧negative electrode collector 505‧‧‧negative active material layer 506‧‧‧negative electrode 507‧‧‧separator 508‧‧‧electrolyte 509‧‧‧outer packaging Body 510‧‧‧positive lead electrode 511‧‧‧negative lead electrode 600‧‧‧secondary battery 601‧‧‧positive cover 602‧‧‧battery can 603‧‧‧positive terminal 604‧‧‧positive electrode 605‧‧‧isolation Body 606‧‧‧negative electrode 607‧‧‧negative terminal 608‧‧‧insulating plate 609‧‧‧insulating plate 611‧‧‧PTC element 612‧‧‧safety valve mechanism 613‧‧‧conducting plate 614‧‧‧conducting plate 615 ‧‧‧Module 616‧‧‧Wire 617‧‧‧Temperature control device 900‧‧‧circuit board 910‧‧‧label 911‧‧‧terminal 912‧‧‧circuit 913‧‧‧secondary battery 914‧‧‧ Antenna 915‧‧‧antenna 916‧‧‧layer 917‧‧‧layer 918‧‧‧antenna 920‧‧‧display device 921‧‧‧sensor 922‧‧‧terminal 930‧‧‧housing 930a‧‧‧housing 930b ‧‧‧Case 931‧‧‧Negative electrode 932‧‧‧Positive electrode 933‧‧‧Separator 950‧‧‧Wound body 951‧‧‧Terminal 952‧‧‧Terminal 980‧‧‧Secondary battery 981‧‧‧Film 982 ... ‧‧Shell 7102‧‧‧Display 7103‧‧‧Operation Button 7104‧‧‧Secondary Battery 7200‧‧‧Portable Information Terminal 7201‧‧‧Shell 7202‧‧‧Display 7203‧‧‧Belt 7204‧‧ ‧Belt Buckle 7205‧‧‧Operation Button 7206‧‧‧Input and Output Terminal 7207‧‧‧Icon 7300‧‧‧Display Device 7304‧‧‧Display Display 7400‧‧‧Mobile phone 7401‧‧‧Shell 7402‧‧‧Display 7403‧‧‧Operation buttons 7404‧‧‧External connection port 7405‧‧‧Speaker 7406‧‧‧Microphone 7407‧‧‧Secondary battery 7408 ‧‧‧Lead Electrode 7500‧‧‧Electronic Cigarette 7501‧‧‧Atomizer 7502‧‧‧Carton 7504‧‧‧Secondary Battery 8000‧‧‧Display Device 8001‧‧‧Shell 8002‧‧‧Display Unit 8003‧ . ‧Light source 8103‧‧‧Secondary battery 8104‧‧‧Ceiling 8105‧‧‧Side wall 8106‧‧‧Floor 8107‧‧‧Window 8200‧‧‧Indoor unit 8201‧‧‧Shell 8202‧‧‧Air outlet 8203‧‧‧ Secondary battery 8204‧‧‧Outdoor unit 8300‧‧‧Electric refrigerator freezer 8301‧‧‧Shell 8302‧‧‧Refrigerator door 8303‧‧‧Freezer door 8304‧‧‧Secondary battery 8400‧‧‧Automobile 8401‧ ‧‧Headlight 8406‧‧‧Electric engine 8500‧‧‧Car 8600‧‧‧Motorcycle 8601‧‧‧Rearview mirror 8602‧‧‧Secondary battery 8603‧‧‧Direction lamp 8604‧‧‧Storage box under seat 9600‧‧‧tablet terminal 9625‧‧‧switch 9626‧‧‧switch 9627‧‧‧switch 9628‧‧‧operating switch 9629‧‧‧fastener 9630‧‧‧shell 9630a‧‧‧shell 9630b‧‧‧shell 9631‧ ‧‧Display unit 9633‧‧‧Solar battery 9634‧‧‧Charge and discharge control circuit 9635‧‧‧Power storage body 9636‧‧‧DCDC converter 9637‧‧‧Converter 9640‧‧‧Moveable part

In the drawings: Fig. 1 is a figure illustrating the depth of charge and crystal structure of a positive electrode active material according to an embodiment of the present invention; Fig. 2 is a figure illustrating a depth of charge and a crystal structure of a conventional positive electrode active material; Fig. 3 is The XRD pattern calculated from the crystal structure; Fig. 4A and Fig. 4B are the diagrams illustrating the crystal structure and magnetic properties of the positive electrode active material of one embodiment of the present invention; Fig. 5A and Fig. 5B are the crystal structures illustrating the conventional positive electrode active material and magnetic diagrams; Fig. 6A and Fig. 6B are sectional views illustrating the active material layer when using a graphene compound as a conductive additive; Fig. 7A to Fig. 7C are diagrams illustrating the charging method of a secondary battery; Fig. 8A to Fig. 8D are Figure 9 is a figure illustrating the discharge method of a secondary battery; Figure 10A to Figure 10C is a figure illustrating a coin-type secondary battery; Figure 11A to Figure 11D is a figure illustrating a cylindrical secondary battery Figure 12A and Figure 12B are figures illustrating examples of secondary batteries; Figure 13A1, Figure 13A2, Figure 13B1 and Figure 13B2 are figures illustrating examples of secondary batteries; Figure 14A and Figure 14B are figures illustrating secondary batteries Fig. 15 is a diagram illustrating an example of a secondary battery; Fig. 16A to Fig. 16C are diagrams illustrating a laminated secondary battery; Fig. 17A and Fig. 17B are diagrams illustrating a laminated secondary battery; Fig. 18 is a diagram showing the appearance of a secondary battery; FIG. 19 is a diagram showing the appearance of a secondary battery; FIGS. 20A to 20C are diagrams showing a method of manufacturing a secondary battery; FIG. 21A, FIG. 21B1 and FIG. 21B2 , FIG. 21C and FIG. 21D are diagrams illustrating a bendable secondary battery; FIG. 22A and FIG. 22B are diagrams illustrating a bendable secondary battery; FIG. 23A to FIG. 23H are diagrams illustrating an example of an electronic device; FIG. 24A Figure 24C is a diagram illustrating an example of an electronic device; Figure 25 is a diagram illustrating an example of an electronic device; Figure 26A to Figure 26C is a diagram illustrating an example of an electronic device; Figure 27 is a diagram of the present invention of Embodiment 1 The XRD pattern of the positive electrode active material of an embodiment; Fig. 28 is the XRD pattern of the positive electrode active material of an embodiment of the present invention of embodiment 1; Fig. 29 is the positive electrode active material of an embodiment of the present invention of embodiment 1 XRD pattern; Fig. 30 is the XRD pattern of the positive electrode active material of an embodiment of the present invention of embodiment 1; Fig. 31 is the XRD pattern of the positive electrode active material of the comparative example of embodiment 1; Fig. 32 is the comparative example of embodiment 1 The XRD pattern of the positive electrode active material of; Fig. 33 is the XRD pattern of the positive electrode active material of an embodiment of the present invention of embodiment 1; Fig. 34 is the XRD pattern of the positive electrode active material of an embodiment of the present invention of embodiment 1; Figure 35 is the XRD pattern of the positive electrode active material of the comparative example of embodiment 1; Figure 36 is an embodiment of the present invention of embodiment 1 And the XRD pattern of the positive electrode active material of comparative example; Fig. 37 is the chart showing the volume change rate of the positive electrode active material of an embodiment of the present invention of embodiment 1; Fig. 38A and Fig. 38B are the graph of the present invention of embodiment 1 The cycle characteristic of the secondary battery of an embodiment and comparative example; Fig. 39 is the ESR signal of the anode active material of an embodiment of the present invention and the comparative example of embodiment 2; Fig. 40A to Fig. 40C are the present invention of embodiment 2 The ESR signal of the positive electrode active material of an embodiment and comparative example; Fig. 41A1, Fig. 41A2, Fig. 41B1 and Fig. 41B2 are the crystalline structure models used in the calculation of embodiment 3; Fig. 42A and Fig. 42B illustrate embodiment 3 The graph of the calculation result; Fig. 43 is the graph illustrating the calculation result of embodiment 3.

Claims (15)

An active material comprising: active material particles containing lithium, cobalt, magnesium, oxygen, and fluorine, wherein, when a voltage of 4.6 V is applied to the active material, an X-ray diffraction pattern of the active material using CuKα1 lines is at 2θ It has a first peak at 19.30±0.20° and a second peak at 2θ of 45.55±0.10°. The active material according to claim 1, wherein the active material particle includes a surface portion in a region from the surface to a depth of 5 nm, and the atomic number ratio of magnesium and cobalt in the surface portion of the active material particle is 0.020 0.50 or more, and the atomic number ratio of fluorine and cobalt is 0.05 or more and 1.5 or less. The active material according to claim 1 of the patent application, wherein the fluorine has a bonding energy of 682eV or more and less than 684.3eV in XPS. The active material according to item 1 of the scope of the patent application also includes a covering layer covering the active material particles. According to the active material of claim 1, titanium is also included. According to the active material of claim 1, it also contains aluminum. According to the active material of claim 1, the total ratio of lithium, cobalt and oxygen accounts for more than 95wt% of all elements in the active material particle. An electrode, including the active material in item 1 of the scope of the patent application. A secondary battery, including the electrode described in item 8 of the scope of the patent application. An active material, comprising: active material particles containing lithium, cobalt, magnesium, oxygen, and fluorine, wherein the active material particles include: a first crystal having a first crystal structure, and the first crystal structure accounts for a charging depth of 0.8 or more 60wt% or more of the whole crystals; and a second crystal having a second crystal structure, the second crystal structure accounts for more than 60wt% of the whole crystals with a charging depth of 0.06 or less, and the first crystal structure and the second crystal The difference in volume per unit cell between the structures is within 2.5%. The active material according to claim 10, wherein the active material particle includes a surface layer portion in a region from the surface to a depth of 5 nm, and the atomic number ratio of magnesium and cobalt in the surface layer portion of the active material particle is 0.020 to 0.50, and the atomic number ratio of fluorine and cobalt is 0.05 to 1.5. The active material according to claim 10 of the patent application also includes a covering layer covering the active material particles. The active material according to claim 12, wherein the covering layer comprises titanium. The active material according to claim 12, wherein the covering layer comprises aluminum. According to the active material of item 10 of the patent application, the total ratio of lithium, cobalt and oxygen accounts for more than 95wt% of all elements in the active material particle.

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